Concepts from other MMOs that would be utterly anathema to FFXIV

[Lauront]

Customization beyond character creation and choice of class, lateral progression, substantial coordination, performance metrics, actually healing, and transparency.

I might even be fine with just having some slightly less clear-cut shared-CD actions and more significant stat effects that are more conveniently set (e.g. being able to choose between two secondary stat choices per gear piece, and choosing breakpoints to keep to between them).

Some jobs have good deal of difference in playflow available to them just by switching between GCD speeds.

In general I'm wary of choices for the sake of choices, but having several playflow variants or a few other significant changes per job can be worth their development costs insofar as they increase the breadth of attraction of jobs that might otherwise be overlooked.

Anything that increases the product of breadth and depth of attraction to players more than it increases the development costs necessary, without decreasing overall cohesion, will likely be good design.

Agree with all those. The healing model in this game, where you're required to dps, but then stuck with really simplistic, dull healing "rotations" baffles me. At the least they could make them a bit more like dps rotations, particularly for WHM, because I can't imagine 1 nuke 1 dot is much fun.

I think specs would be very hard to implement given their job model, but the sort of individuation you mention would be a welcome addition.

Major leader figures dying, staying dead and being replaced by a successor who may very well cause strife for the people that they're leading.

I'll add to those, the greater focus on races that some MMOs have, like racial starting/home zones/cultures and the like. I'm not too fond of this game's preference for trying to put that focus in the cities and it can lead to certain races' lore being shoved into the background and things feeling a bit same-y. They've improved on it since 2.0 but the damage has been done.

Another would be classes (="jobs") focused on the "fight fire with fire" mindset, like WoW's Warlock, Demon Hunter, Shadow Priest or Death Knight, on the shadier/more morally grey side of the spectrum... this game has little like that. It's partly due to the lore on aether, but also because of the character's role in the story. Even BLM and DRK are rather tame in this regard - the closest would be something like Void Mage or Necromancer. I'm hoping with the end of the Hydaelyn/Zodiark saga they'll begin taking a few more liberties, but I somehow doubt that they will.