I really hope they don't just raise the level cap to 110...

[Shistar]

I wasn't worried about the lore aspect at all, just purely how it would work from a gameplay point of view with your actions and traits, where the above is the closest you get to hitting on it, but don't really answer the question.

I think a lot of what I was proposing got misunderstood because I wasn't able to go into too much depth in the first message (and got carried away with the lore, because it is what I like most admittedly). I'll try to clarify what I meant in order:

If I am a player that is level 100 going into this expansion with it's new level system, what happens to my current kit? Do I keep it all or do I lose it?
Then you have to ask, how would a new player experience this all if they were to start from the second levelling arc?

For this kind of system to work, it is likely that jobs would be partially revamped, as was mentioned anyway by YoshiP. Nothing is set in stone yet and we don't know what to expect, but there were mentions about working on jobs so this would be the ideal time to remove some of the fat and get a cleaner slate for the next arc. Much like it happens when a job is revamped, veterans can expect they'll have to sit down for a sec to check out their new skills and reorganize their hotbars.

I would temporarily split veterants and newbies in the MSQ:

• Veteran players would stay as they are, so to speak, without any tutorial or anything. Their x.5 MSQ cleans up anything left from the previous expac and puts them straight into the new arc.

[...]An alternative would be to strip away the level 100s kit so that they have a much more simplified kit, but I'm sure you know how well that would go down.[...]

• Newbies are placed in a variant of the x.5 MSQ instead of straight into the next arc, where they are taught some basics to get them going. They'd unlock skills as they hand in the quests as to not drop all of their kit on their laps immediately, and I'd place 1-3 solo duties to get them accustomed to their buttons. By the end of this version of x.5 they will have the same kit as veterans, but they would have unlocked it quest by quest to give new players a chance to get their stuff in order without overwhelming them.

In this version I am imagining, I expect stuff like 1-2-3 combo to be able to be collapsed into a single button, actually descriptive tooltips for your skills, skill upgrades collapsed into a single skill (Cure I and Cure II would become a singular skill that changes based on your synced level, as an example) to trim as much fat as possible without making the job unrecognizable. All of this would be optional of course, but would be enabled in the default HUD with the purpose of making the newbie onboarding process a little smoother.

[...] and, just to be clear, just having a simple training tutorial isn't necessarily good either as if a job changes, it will need to be updated alongside the job, unless you give very basic info, which, again, I don't see being helpful.

Yes, the tutorial part would have to be tweaked as jobs change, but the basic structure will remain the same and it won't be too bad to tweak as time passes. It is important that they keep this part updated and useful for new players, so if they want to make a new starting point then it is only expected they don't make it once and forget about it.
These tutorials would be in place just to tell newbies what their buttons do to a basic enough level that they can interact with their environment (learn about mechanic markers, interactable stuff, quest types) and learn the rest during their journey, like we did back then because we didn't even have a tutorial telling us what to do. It's not meant to be as braindead as Hall of the Novice but anything with too much in-depth text and you'll bore them to death before they even begin. Some practical exercises disguised as quests and duties is enough, what I mean is you'd be doing the "leveling" of your job as you go and in the end it'd feel much like the 10 levels you gotta grind before starting a new expansion with the newly released job. Most of us learned what our skills do by going up to a mob and pressing it to see what happens, I don't see why they can't do the same.
I won't get too much into detail on what would be a good or bad tutorial, but as I mentioned before Tomb Raider II wasn't a terrible example considering the game's age.

You mentioned the open world, different level scales based on which arc you are in, but you then cannot have the max level players and the low levels in the same instance as they cannot scale a mob based on who is hitting it, so you are effectively doubling the amount of areas you need, one for if you start arc 1 then do arc 2 and another set for is you do arc 2 then arc 1.

No, you misunderstood me. No such thing as multiple instances and player separation. Your character would be synced according to your level in the expansion. Let's see it this way:

We have two parallel leveling systems, much like your MSQ lvl, your job's level and Eureka's Elemental Level are three parallel levels that your character keeps track of. MSQ level would be split into arcs, so Arc1 (ARR-DT) and Arc2 (All expansions related to this story's arc)

Let's say we have two players: Player A's stats look like this:
MSQ Arc1 lvl100 (endgame)
MSQ Arc2 lvl20 (endgame in this example)
Player A is a veteran that has multiple jobs fully leveled up.

Player B:
MSQ Arc1 lvl1 (never touched it)
MSQ Arc2 lvl20 (current endgame)
Player B only has their starter job at current level and also has access to the expansion's 2 jobs, which may be leveled to Arc2 lvl20 as well.

When Player A is in any area, their level will automatically sync to the relevant arc's level (in Thanalan it'd be lvl100, in a new expac's area it'd be lvl20), much like your level would automatically swap to Elemental lvl60 in Eureka Hydatos and forget all about your actual lvl100 in the overworld.

When Player B is in a new area, they will also be lvl20. When they enter an area belonging to Arc1, they would be afforded a sync down to the area's minimum level (or a couple of levels below the minimum) and to a maximum of Act1 lvl30. They would only have access to the ARR areas and this level sync would be only to prevent them from being oneshot instantly by a lvl10 ladybug, but they'd still get their butts handed to them if they're not careful; much like a healer can't peacefully go through Aurum synced without getting killed. If Player B then goes through Arc1's MSQ, their level will increase and when they surpass the area's minimum sync level they will no longer be synced and simply use their real Arc1 level instead. Player B would then get access to the rest of ARR+ jobs starting at their expected level so they can have the OG experience if they'd like. If they don't wanna level the job, they can buy a skip for it.
Only weird exception is HW jobs because they are stuck in Ishgard, which might either be a motivator for new players to check out Arc1 in order to get their hands on these jobs or it might be a point of frustration for those who don't wanna touch Arc1 at all. Stuff to think about here, but it's always been a point of frustration.

There's also another point I think you'd be about to ask which is that Eureka's Elemental level applies to your character as a whole rather than your jobs, while this system would most likely apply to a singular job in the Arc1/Arc2 system. I am not too worried about this myself since players would have a perfectly functional job for endgame, they can get their hands on other jobs and level them much like we'd do normally. If Player 2 wants to have all content available to them without going through Arc1 manually, a story skip would be available and then they just have to get the last 10 lvls done as usual.

Then we get into instances, like dungeons and trials. Would the level 100s play with the new players? The level 100s would dominate and the new players would be useless. So you would necessarily have to split them up, which divides the community.

Yes, everyone plays with everyone and you just get synced down, same way it happens when you enter Sastasha for a sprout's first dungeon. The difference between a (synced) max level, max gear player vs. the sprout that showed up in min ilvl will always be there, but there shouldn't be the difference you're talking about and in gameplay it'd be like doing any other dungeon. Things would work as normal.

If you are wondering what happens when Player B queues into a roulette, they won't magically have duties from Arc1 if they haven't unlocked them. They'd have to go back and unlock them through Arc1's MSQ.

Going back to the previous topic about MSQ levels applying to your character or your job, how you'd tell the roulette if you'd like to level your Arc1 or Arc2 levels is beyond me unfortunately. I would assume you need all Arc1 levels before you can level up in Arc2 if the job belongs to Arc1, then any jobs introduced during Arc2 get their headstart as usual. The roulette would work normally from here, not queueing you into anything higher than your lvl/ilvl and handing you the appropriate EXP. Example below:

Player A has NIN Arc1 lvl100/Arc2 lvl20, RPR Arc1 lvl100/Arc2 lvl10, and a new job from the current expansion, let's call it Corsair for fun (CRS) at starting level (lvl90)
Player A queues into a roulette as NIN. They gain no EXP because it is maxed out on both arcs. But if they queued as DRG or CRS they'd gain Arc1 EXP until lvl100 (in CRS's case), after which they'd start gaining Arc2 EXP.

What are you getting from these new levels? If they are to be upgrades to what we currently have, then the new player needs access to everything a level 100 has, which, see above. However, if it is a completely new set of actions, then the level 100 would need to start from scratch otherwise, they wouldn't use the new tools as their current kit would be so much better, unless you restrict access to them, which again, see above.

I might be missing something, but I don't see the reason why new players would be so clueless as to be unable to figure out their buttons if they are explained to them, they have a chance to test them out and you give them their kit bit by bit so they can get used to it. They'd have their basic stater kit (1-2-3, dot if applicable, basic heal/mit if applicable) + they'd obtain the rest as they go through the introductory quests until they're caught up. Instead of learning one or two skills every 5-10 levels, they'd be learning them at a much faster pace but they'd also have NPCs actively letting them know about this and telling them to check tooltips, try out the skills, etc.
What happens when you unlock a newly introduced job from an expansion, such as SGE or VPR? You have a bunch of new buttons and your job quests, so you sit down for a minute, get your skills in order, do your quests so you can get some sort of explanation on them and then you're off. I don't think we should baby new players too much, give them the tools and they will figure it out just fine.

Then we have the fact if you do just give everyone the level 100 kit upon starting this new arc, that is basically level 110 with a free level skip for a job for new players, just with a new name. If I am missing something, feel free to let me know, as I probably am, but as you can tell, I have so many questions where, in my mind, this whole thing has basically boiled down to making it level 100 with a free level skip.

In the end, this is what some people are asking for, I'm afraid. If you give them a new starting point but you also want it to work for veterans, but you don't want veterans to lose any of their kit, but you don't want new players to have anything, then what is left? How do you get these two groups of players to coexist? What people want is a way to catch up to endgame faster, so something has to give.

My idea essentially nerfs them if they're in any area that doesn't belong to the arc they did, and actively blocks access to areas you must unlock through MSQ. I'd imagine SE's marketing team would have a blast selling you different Arc Starter licenses, or Arc1 + Arc2, Collector's Editions, etc. A new player would likely buy Arc2's starter kit and have the option to add Arc1's expansions to their account later on, along with their Collector's editions and stuff. They'd probably market the new Arc's pack more aggressively to prevent people from accidentally buying ARR and wondering what happened.

Back to the job skips...
Giving them a tutorial, a singular job from the classic roster (meaning ARR only, most likely, considering the rest are unlocked by buying their relevant expansion and in HW's case you have to reach Ishgard too) and dropping them in the same spot as veterans would still put them at a disadvantage because they're learning the ropes 100 levels later, but it is a way for them to get "straight into the action" like many want. One could imagine that if these new players then want to play, let's say, Samurai, but don't want to go to the previous arc to physically unlock it, level it manually, etc, then SE still gets their job skip sale and they have a new player that is staying instead of possibly having quit halfway through ARR.
This would essentially give them one job level skip to 100, but they'd have to buy all previous expansions to actually make use of this skip. They'd probably market the Arc2 license to "include" this job skip to get you straight into the action, but in truth if you want anything besides the jobs accessible to free trial players in main cities + the 2 jobs included in your Act2 pack, you'd have to go to Act1 and unlock them yourself (or buy the relevant expansions and skips)

It is not the most elegant solution, I didn't claim it was by any means, but I was just throwing my idea out there. I don't think SE would bother ever adding a new start without being well aware it'd put their story skip sales in jeopardy (although I think this idea verges on greedy enough for them to like it), so this is just throwing stuff at the wall for fun.
Thanks for reading it and giving it a thought! I'm looking forward to your thoughts on this, I hope it helped to clarify the idea a little bit more.