Just a couple of things come to mind when I was looking through stuff...
1) Some way to get crafting / gathering materia through combat resources. It's very weird to have the crafters able to make combat related gear and even be the primary way to overmeld gear, yet there is no indirect support to aid people doing content that demands the crafted gear.
2) The odd level materia is in a kind of weird place and wouldn't mind seeing it just take a hike. The only point where it ever gets used is overmelding, which is only useful on crafted combat and crafting / gathering gear. Eventually you end up inundated with the stuff and nothing to do with it so it just takes up inventory space.
3) Have the daily beast tribe quests scale until level the 71st, 81st, and so on along with any fates.
4) A vendor where we can rebuy dungeon armor we've found before so we don't have so many sets of armor in our inventory. We already got achievement tracking and it would make it a lot easier to add collector based achievements as well.
5) Baseline all ARR and HW jobs so that the starting set of skills is what they got at 50 rather than level 1. Even new players can probably figure out how to run a level 50 character in this game given how simplistic those are to operate and the content. There's no point to the extremely limited skill availability at sub 50 anymore.