Most of mine have probably already been said but:

1. Class reworks across the board - many classes have lost their individualism in what feels like an effort to make them simpler to play or balancing (i.e. Summoners, Healers especially). Some of the unique spells/abilities have been removed, playstyle pretty much made the same, etc. I'd like to see the classes get reworked a bit in keeping with their lore (i.e. Summoners - give them more summons, make the summons actually useful rather than been a non-targetable pet that fires off abilities that you could just give to the Summoner) and make them a bit more unique again. I appreciate my experience with classes is small but so far some of them feel a bit 'shallow' during play.
2. Rework BLU - remove the limited job rubbish and make it a properly playable class. It worked in FFXI - it can work here with the correct thought/setup.
3. New classes? I'd like another healer (providing point 1 is taken to heart and it's not made too generic) and maybe BeastMaster would be cool if pets were properly reworked/utilized.
4. Rework glamour system - increase the glamour slots/armoire or have glamour options not actually take up space anywhere. (Maybe something like WoW where once you have equipped a piece of armor it becomes a glamour option automatically?). I'd also like to see gender/class/job restrictions removed on glamours - allow us to glamour to anything, would really bring some interesting options to the table (plate wearing Healer?)
5. Sort out MSQ in early levels (i.e. ARR and the drag between expansions) - this is a more of "it would be nice" (appreciate there are limitations to what the devs can do without a full overhaul) but as a new/returning player levelling (or someone levelling an alt) these areas feel drawn out and a bit tedious. I know many a person who has nearly quit before reaching Heavensward because they get burnt-out/bored with the quests.
6. More unique quest types - SB and ShB have brought us some different quest types other than the usual "Kill X mobs", "Gather X things" - without spoiling anything there's some fun quest types involving darts, psyching up an NPC via dialogue options, playing as an NPC, etc. which I found to be fun and a great way to break up the usual grindy quest types. I'd love to see more stuff like this going forward.
7. Housing - it shouldn't be so difficult for someone to get a house.
8. More customization options on characters - especially original races - give us more face/eye/jaw/nose/etc options, more hairstyles, tattoos. Whilst you're at it add female Hrothgar and male Viera in. I want Bunny Bois!