Sitting Positions (Simple, Animation)
There are plenty of NPCs already have unique sitting positions; it'd be nice to be able to use emote commands so that when your in a sitting position you don't look like you've had a brain aneurysm

Better class customization (Complex, Gameplay)
With cross-class skills your afforded some different customization, and with the rare chance you can use materia your offered it again, but over all your looking at the same cookie cutter builds. I'd like to see different play styles for different jobs. The warrior for example, could have two different splits, one where its focus is Damage, another for Tanking. The Paladin could be split between Tanking and Healing, Monk could be split between Support and Damage, etc. etc. Each job has the potential for these kinds of different specializations, which don't necessarily pigeon hole you into a certain play style.

Uniqued/varied items and gear for grinding/dedication purposes (Complex, Gameplay)
The current beastman factions are neat, I'd like to see more of it and spread out across the entirety of the game. Quests, factions, rare item drops, etc. all of it to give you a sort of focus or end game goal to work towards besides collecting the same gear every one else has.

Improved PvP (Complex, Gameplay)
As it stands right now PvP isn't all that great; it can take forever to random queue for it, and it's just kind of like a poor mimic of WoWs Arena system. I'd like to see something more akin to battlegrounds, larger fields with a game actually played that focuses on the characters competing against one another. Also an improvement to the Arena system, perhaps a spectators area where you can watch matches and place bets on them, or something.