I would really like to see more of the other party members: Quistis, Zell, Selphie, and Irvine should get more character development.
I would like the battle system to be redesigned to allow for more character diversity outside of the Limit Breaks. I find that character diversity is a positive attribute rather than having every character be a jack of all trades.
Wolf Kanno had some great ideas. It's not asking for that much if the game was really going to be remade!