I would honestly REALLY dig a "Kingdom Hearts" crossover event

[Avoidy]

This sounds cool. I'd love any of Donald's endgame staffs as a BLM weapon, some of those are sick looking.

[Sililos]

Argh keep KH out of FFXIV. No thanks to this event.

Last thing we need is that convoluted crap, they ruined FFVII Remake, dont let them touch FFXIV!

[Vav2021]

Argh keep KH out of FFXIV. No thanks to this event.

Last thing we need is that convoluted crap, they ruined FFVII Remake, dont let them touch FFXIV!

what did they do to VII remake?

[Elizar_Naki]

This is a crossover I've been wanting to see for ages. Unfortunately, due to Kingdom Hearts being a joint Disney/Squeenix venture, actually getting it to happen would be a copyright nightmare since Disney would also have to be convinced to sign off on everything. Also, as someone with a more conservative mindset, I'd agree with an earlier post that Disney has been garnering themselves a lot of...questionable press recently, so it might not be in Squeenix's best interests to bring their affiliation back to center stage for the time being. Still, it's fun to speculate, so I'm gonna add my version to the mix.

As far as story, this event USED to write itself, as having the Ascians using the Heartless to sew some extra chaos feels like it would've been the most natural thing in the world. The writers could also have included Sora as an extra protag during his self-teaching days between KH3D and KH3, or bring in Riku and/or the Wayfinder or Twilight Trios in the wake of KH3's finale. However, with the Ascians basically gone now, Yoshida's team would have to either make some excuses for why a few of them are still hanging around or find themselves a new catalyst for bringing the Heartless to Etheirys. Neither of these would be particularly HARD, mind you, and the former would probably be the easiest way to make the event accessible to players of all levels, but it's still something the writers would have to think about and (maybe) craft alternate dialogue for depending on where players are in the MSQ.

Cosmetic rewards could be all over the place. I'd personally love my own Keyblade Glider mount or a suit of (preferably dyeable) Keyblade Armor more than the more recognizable black coats or character cosplay outfits, but I wouldn't say no to a bit of both. They could also do something similar to the Monster Hunter collab and craft original outfits--things with very KH-style elements like the armor accessories worn by Terra, Ven, and Aqua, but in more of an Eorzean style of attire. The sheer number of minions they could put out with a crossover like this is similarly staggering given the sheer volume of main characters on both sides of the Dark Seeker saga conflict, and I'm not even gonna weigh in on which of those cast members are most deserving of minion spots.

But most of us who'd want this event would be all about the weapons, so let's go over how I think those should shake down for both Keyblade and non-Keyblade options (there are a lot of other things I wouldn't mind seeing; these are just the ones I think would be most widely accepted by the player base as a whole):

-PLD: this is a job that's all about light and holy stuff, so from a Keyblade perspective, the Kingdom Key (maybe its D variant too), Oathkeeper, or one version or another of the Ultima Weapon would be most appropriate. The Dream Sword would also be a good non-Keyblade choice. Shields could either be the Dream Shield, Frozen Pride (Vexen's shield), Knight's Shield (Goofy's default), or something else from Goofy or Vexen's armory (including a Save the King variant).
-WAR: from a non-Keyblade perspective, you'd either want to use some variation of either the Lunatic (Saix's claymore, since he's definitely a berserker type) or the Skysplitter (Lexaeus's axesword, the closest thing KH has to an axe). Keyblades would be harder to choose from, but OP's Fatal Crest suggestion would be decent.
-DRK: from a character/power perspective, you're looking at either the Kingdom Key D, Oblivion, Way to the Dawn, Braveheart, Earthshaker/Ends of the Earth, or Chaos Ripper/Darkgnaw designs; Xehanort's No Name or the Keyblade of Heart would also be good options, as would the Fenrir due to its size. For non-Keyblade options, we have the Lunatic again or the Soul Eater.
-GNB: the easiest choices here would be the Lionheart and Sleeping Lion Keyblades. However, given that Riku, Terra, and Aqua all utilize the Bladecharge command style (used by Squall/Leon a couple times and also visually similar to GNB's Danger Zone/Blasting Zone ability), any of their Keyblades could also be used. For non-Keyblade weapons, the Soul Eater would work given the above logic, but other than that the only option is the Revolver, which we already have as a glamour.
-WHM/BLM: weapons for these jobs would work off of similar logic as far as their KH counterparts go, so I'm lumping them together. Keyblade options here (and for a LOT of jobs from here on) would have to be Keyblade transformations, similar to how a lot of the FF13 collab weapons were "inspired" by weapons from the actual game. Since Aqua and Kairi seem to be the Keybearers who focus most on casting, things like Rainfall/Stormfall, Destiny's Embrace, or Brightcrest (my personal fave from Aqua's collection) would work best; magic-themed Keyblades like Starseeker or Spellbinder would be good too. The Dream Rod, Mage's Staff (Donald's default), or one version or other of Save the Queen are about the only non-Keyblade options.
-SMN/SCH: lumped together for the same reasons as above, especially since they share a base class. Namine's sketchbook or Zexion's Book of Retribution would be the go-to here, and I...honestly have no idea as far as Keyblades go. Maybe something based on Spellbinder since it has a book-shaped charm.
-AST: an astrometer based on Luxord's Fair Game would be my first choice. Maybe something Lady Luck-themed for a Keyblade choice.
-SGE: Wingblade command style. That is all.
-MNK: this one might be controversial, but I think Larxene's Foudre would be the best non-Keyblade choice. She might be Org.13's ninja, but her stance and the way she holds her kunai are a bit more monk-ish to me. Any of the Olympus-themed Keyblades would work here since Herc is very much a punch guy, or the Knockout Punch due to the name and boxing-glove theme. Or the Happy Gear's Agile Claws form, or Crystal Snow's Blizzard Blades.
-DRG: Xaldin's Lindwyrm would be the obvious choice. Follow the Wind's Flag Rampage form is the only Keyblade spear I can think of.
-NIN: personally, if I didn't get an Oathkeeper/Oblivion combo for my NIN, I'd be upset; I could also see a dual version of Wayward Wind just for the grip style. Non-Keyblade options would be the Foudre again, Xemnas's Interdiction blades, or Young Xehanort's ethereal blades.
-SAM: Eraqus has a very samurai-themed design, so his Master's Defender has to be on here; Guardian Soul and One-Winged Angel also need to be included for similar reasons. I actually can't think of any non-Keyblade choices this time other than MAYBE Mulan or Auron's swords.
-RPR: Marluxia's Graceful Dahlia. Maybe one of the more flower-themed Keyblades to go along with it.
-BRD: something based on Demyx's Arpeggio, or the Fairy Harp or Counterpoint Keyblades.
-MCH: one of Xigbar's Sharpshooter arrowguns, or their combined rifle form. Sora's Shooting Star Keyblade already has a dual-gun transformation, so the Keyblade option would just be to import one of those models.
-DNC: I can't think of anything that would work better than Lea's frisbees or Axel's Eternal Flames chakrams. Even the best Keyblade options would revolve around the Axel-themed Frolic Flame or Bond of Flame somehow, though I could also see the Photon Debugger or Dual Disc Keyblades being a good source of inspiration due to...well, Tron identity disc stuff. Happy Gear's twin yo-yos form would also be amusing.
-RDM: Keyblade options here would go back to the WHM/BLM options, though with the rapier section being the actual Keyblade and the floating orb thingy being the keychain; All for One would also be a good choice due to its Three Musketeers/rapier-themed design. Once again, I'm at a loss for non-Keyblade options, though I guess Mulan's sword would work since she's...kind of a Red Mage?
-BLU: I'm not even considering options here due to how few weapons BLU already gets. I'd just be going back to the WHM/BLM idea well anyway.