Seasonal Events
Seasonal Events in FFXIV tend to be quick one and dones. Now on one hand this is handy as it does allow players to start even 3 hours before it ends and actually get the items, but on the other hand... It's paper thin content and that means you hardly 'feel' the event existing. Like someone sneezed a bunch of decorations but forgot to invite your heart to the party.
So here are some general thoughts:
1- ALL seasonal rewards return each season; however, returning items will be timed life IF you haven't achieved the achievement associated to them. Timed life meaning they last until the season is over, and then the items self delete. Perhaps to make them easier for the system, and players, these timed items are not equipment but are items that apply a BUFF to the character that glamours over your glamour (until the buff is gone). So if you use the pumpkin head item, you get the pumpkin head graphic until you cancel / lose the buff. Those who already have the achievement can buy the items from the vendors in both formats (permanent, can glamour whenever you want, and castable buff item).
If you want the castable item can have charges too, like 5 charges (infinite charges for achievement earned players, please create a Toy Box like WoW and toss this into there- which you also earn when purchasing the item from the cash shop). All seasonal items naturally cost seasonal tokens to purchase. Please don't noob trap a new player into spending all their tokens on temporary items when you secretly put in the current season's items in there that they missed (so ensure the "current" season is rewarded via the quest OR is simply reaching certain thresholds of tokens, so you can't noob trap yourself).
Reason: This allows SE to continue to cash shop the items (I'm not in love with it, but I know money is money lol), while also allowing players to get a much fuller list of cool things to grab and dress up as. Also the BUFF based glamour may be more convenient for players (ensure the buff doesn't get removed on zone transitions, combat, and logging in and out, only if you manually cancel it or the holiday is over). Particularly it will cause a bit more players interacting with events too, because someone might come back around to get a different costume or recharge their witch brooms.
May do housing and mount items too.
2- Add mini-games and other content, never remove this (build on it each year).
3- Convert excess tokens into poetics and or perhaps moogle tomes if that is active at the same time (can set a conversion rate limit, so each day you can change 5 seasonal into 5 moogle).
Right so here are some more event specific ideas (I'd like to hit at least Halloween and Valentines, but will do them later):
Winter ('Christmas') Holidays:
Snowpiles - are in towns and housing areas. Players may interact with the snow pile to start a basic game of dodgeball with other players, and NPCs (especially if there are less players), in specific regions around the piles. Playing the game will reward a Joyous buff that increases movement speed and exp by like 5% for 24 hours, this can stack to 10%. Repeatable quest to participate for additional award (like /additional/ token). Perhaps rewards bicolor and or /rested/ exp as well. Thought that many travel fast but are projectiles, so you can dodge them to an extent (balanced with some special snowballs that fast cast, others you need to hard cast, etc). Just a few buttons 4 - 8 but enough to give a little bit of tactic and 'play'. The mechanics here can also be parsed into one off items (as exampled down below). Larger games can be held in cities on timers, so players can gather together, and might have a bit more controlled chaos (like smaller games are really just chaotic goofiness, but every so often you'll get best of three CTF in a city or something).
Caroling - A daily quest (and FATE) that has you go to a random housing ward (picked based on player activity, will try to avoid dead ones) and play the musical mini-game that is in the game at a few players houses. You may choose to do this in the Ishgard NPC ward, if you hate players lol. Grants the player house a present at their house sign (pile grows at set intervals, so like you might login and have a huge pile). Opening them has random items, thinking of seasonal based toys. This is one of the ways to earn seasonal tokens, for the singing player. Once you reach a certain skill of caroling, which will be remembered each year, you will also get random missions to sing to custom delivery and other noteable npcs. Custom delivery npcs grant progression, other npcs will have their own specific rewards.
Moogle NPC Mail - ALL players may 'randomly' (some sort of range with lower and upper maximums) receive mail from NPCs in the game, this list will range based on your MSQ and side quest story. You can copy these letters into item format, if you want to store them as memories (maybe you're a crazy Tataru lover, and getting a holiday greeting from here meant a lot). There will be a note, in the style of that character, and similar presents like the above. Daily quest to help the moogle post will also grant you some of these presents (delivering to NPCs), which you can trade, mail, or open yourself (due to this some interesting rewards can be placed in there without it feeling like "if you don't have a house, you're SoL").
Last Minute Moogle Drops - Angled down view, players have houses they fly by that they have to toss the correct presents down to (few options), while also using the move keys to strafe into different lanes to collect bonuses and dodge hazards (like a temple run or other run type mobile game has lanes). Chance to get NPC mail forwarded by moogles from those whose cheer you brought (which can contain little goodies themselves).
Lighting / kindling ceremonies - Daily quest to travel around town to bring power and set up lights (use phasing, like beast tribes) and other decorations. After the items have been set up (all players move to MAX decoration phase after a certain day), you can continue to do the quest as a rekindle / maintenance type angle. Maybe for the decoration part, there is a personal phasing system but relies on the entire server's progress. So for example the first 5 days is decorating, and as a player I've done no decorating quests, but the server has done a bunch so the server is on tier 2 (lights and trees in many locations); this means as soon as I do the quest twice, I am also on tier 2. Make sure the max phase is peaked at the core of the holiday and lasts long enough that people can enjoy it visually. Each region will get a buff based on their status. For example at tier 2 all rare / exclusive items drop rates for the associated zone is increased by 5% and movement speed by 5%. Tier 3, all FATEs count as double completion and have a chance to drop seasonal items (up to 10 fates a day).
To add to this buff ideas, as I think it would be fun. Each region will get a skeleton buff system through the decoration / server teamwork, but additional details of the buff will be added by players doing seasonal content. For example if you're ice skating in a region, after 30 seconds you contribute a little to the joy of that region. So the buff might go from 5% movement speed to 5% movement speed, and if wearing seasonal items also double beast tribe progression, 10% faster movement speed, and 10% faster GP regeneration. Or like for ARR relics, you get double light.
Ice Skating areas - slidy mechanic spaces, mostly for goofs in the cities and in some contextually logical locations in the wild.
Use the drift / slide mechanic in the open world as well, where it visually makes sense (like A SLIGHT, VERY SLIGHT version lol, effects on all ice in the game, so players catch up a bit of speed (25% increasing over duration of movement, feeling like momentum) and very lightly slide (180 might slide you the opposite direction for a second, but turning wouldn't be an issue, movement skills will maintain momentum and can turn you on a dime). Such that it's really a neat benefit / neat thing and wont turn into accidentally sliding across the whole zone while afk.
Chocobo racing will get seasonally impacted visually - and bonus progression for the first few runs each day. There should be some sort of chocobo content on a rotational as well (like Chocobo day / week or something).
With all mini-game ideas, these systems could / probably should be written so the systems can be reused for other mini-games (like in the saucer). So a snowball system, upgrade / changes to chocobo driving system, might turn into a tank game (world of tanks or whatever that game is called), or you might get bomber man like stuff... Attempting to make the systems reuse-able can help them be useful.
Some seasonal items:
Presents - akin to the bozja, and other lootboxes, except with seasonal based items.
like:
One time snowballs (with variants (see Grumpus item below), these can use ideas from the general snowball mini-game above but can be used outside of the mini-game, and in general these items will shortly UI identify the player that threw it so you can get them back!)
Variants: hard packed one might create a dazed effect on the target for a second.. maybe a 1 or 2 second mild slow, enormous which will roll and move players (rare), trick-shot which identifies a spot near where it could be (fuzzy marked), etc
One time flurries and fireworks that have a winter vibe
One time blasts of cold wind that lightly move players (will not move them in fall damage zones)
Temporary Snow drifts and paths - will apply a SLIGHTLY slidy effect and movement speed buff, if you slid over the drift you catch a little air (doesn't immediately drop you to the ground). Sled and skates will take much larger impact from these. Players can place them, they last for a little while.
Coal, can be used to apply a dirty effect to self, if placed in a present or mail will automatically apply on open (will only work to friends)
Rocket Skates - below skate mechanic, on steroids. One time
Rocket Sled - same deal
Assortment of different
theme'd candy - all coming with minor buffs that last 30 or so minutes, from 5% movement speed, 5% rested bonus, free teleport, etc.
Chance for
toy variants of certain items (like pocket snowballs, which grants you 5 snowball buff and you can then with a button that appears throw 5 snowballs in sequence)
Interactable Drinks and food, in Inns / taverns. Add seasonal drinks to the shops. (Like in OP, make the drunk effect when drinking 'goof' alcohol items). Buffs ranging from the classic EXP buffs to cuter goofs like
Uplifting Bubling Cider that raises your character off the ground slightly and reduces non-target based damage by 10% for an hour (does not work in non-echo-able content). Make the player placed items have double duration (so if your FC goes full holiday, that's awesome).
Frosty Snowman 'type' - one off item that transforms you into 'insert' type of snowman. As many different styles as SE feels, could just be one, could be size based, could be race, etc. Just.. transform into a snow man. Increases Ice damage resistance by 50% and decreases fire resistances by 75%, increases slide acceleration and control (resistance buff works outside of non-echo-able content, that's assuming they still track that resistance data.. they might have stopped since removing it generally from the player sheet lol).
Holiday mounts - all of them travel faster based on the seasonal joy of the region
Special Someone Gifts - Once per day you can give a custom delivery NPC a gift to get a free high quality 'turn in'. If you're partnered/married you can also get one for that (increases healing and duration on buffs casted on each other outside of non-echo-able content).
Stockings - Like by the fireplace, not Soken Knee High

. housing version of the present box system. Can set rules to FC, friends, or party only. Can only open public stockings every so many hours (friend is unlimited).
Permanent Drifts, Paths, and Skating Rinks - Housing items.
Sled - toy / mount with slidy mechanics, where going down hills will speed up, up hills slows down, and there is some cap on turn rate. Will launch you off cliffs and edges. For maximum chaos, remember where people launched off edges and if they land on something unpathable (like an area you can't land on but can fly to) give them a magical sphere of snow under their bottoms and the ability to teleport back to where they last touched pathable ground (and they can also cast /return / teleports).
Ice Skates - Different colors / types, with a special magical one allows you to do it 'off ice' (might generate ice underneath, this effect once made can be used for other stuff-- like sand skating as part of some other item idea). This will use a system similar to the sled but with different characteristics (ability to pick up pace, like a chocobo carrot / stamina system almost) and better turn radius (slower than a sled down a hill though)
Grumpus - prevents any holiday effect working on you, toy. Never exclusive to the cash shop. (Applies Time Out buff that has no visible timer and expires at the end of the event, may be canceled, doesn't remove from changing zones, logging out, dying, etc- can still do the daily quests, just can't be the target of random player fun).
Perpetual Snow Cloud - produces a snowpile at the target location after 5 seconds (snowing), uses the snowpile mini-game. Some many hour cooldown (10? 24?).
Obnoxiously Life Size Snow Globle - puts your character into a snow globe, with the visual effects you might expect. A small circular space you cannot escape from (you can cancel the buff to leave). Jumping and moving will increase the snow effect, which will slowly settle if you stop (not 'physics' per say, just watches if you move or not and increases or decreases the effect).
Wind-up Flurries - gives your character some wind effect (the physics on gear), cold breath, and some visual sfx for wind and snow.
Spacious Box - may put an item inside it and have a player open it. Charges. When used you carry the present in your hands until you get rid of it (trade, mail, etc). You may set it down, if you do so it'll ask if it's open to everyone, party, or only friends list (and lasts 15 minutes). You can pick up your own box, getting the item back but not the box. May only put down a box every so often, and may only pick up so many PUBLIC ones as well (represented by buffs). Box costs seasonal tokens. Lalafells fit inside.
Magically Returning Box - toy, generates a timed life box. Long cooldown. Can be used outside of the season.