The most important UI change that needs to happen is the damned game needs to not purge our HUD settings on any element we don't use frequently. HUD settings are saved client-side, so there's absolutely no sensible reason why, when changing back to a job I haven't touched in a while, I have to re-change the job gauge back to simple mode and re-position it where I want it. There's no reason why, going back into Eureka, my elemental wheel and logograms need re-sized and re-positioned. Etc.

When I save HUD settings, I want those settings saved, permanently. Not "as long as you're using them."