In case we want to talk about new features we'd like to see that wouldnt require fundamental changes of the game:
I'd like to see the option to redo any quest in the game. Without getting the rewards, ofc. Just doing the quest again - a lot of sidequests are telling great stories and in a singleplayer game I would probably have a savegame that would allow me to do that quest again without playing through the whole game. Doing 2.X Hilli again? Yes, please!
Frankly I dont know why this isnt already in the game - we even have a character in the game that could give us the quest: The Wanderin Minstrel, whos singing about our adventures and telling our story.
So what I'd like to see is: Go to him, pick the quest(line) you want to do again, get the quest from him, follow the quest normally but without getting any rewards (no exp, no gil, no gear - just the quest).