The first thing I would change is to get rid of the MMORPG system. I know they want to apply to a bigger audience and that it worked out big with Final fantasy VII, but this is not what people want. Since the Playstation 1 revolution, Final fantasy gamers buy the games for the story, however it might be turning more into an emo soap with every new game, it was still what we buy them for. If we want to spend an hour leveling up between story parts, we would’ve bought an MMORPG game to begin with. This, to put it simply, has got to go. There are no people in an offline FF game to brag your level to, or for whatever weird reason you might have to spend several hundreds of hours leveling.
As an adding feature, we bring back the materia system and old battle system. I’ve played a lot of FF games in my time(8 in total), and besides the class-system(for magic), this is still the best one. The class-system was a well-balanced system, but it belongs to the oldest generation of FF-games. I say we let the legacy stay intact.
As a new feature, when using the old-style battle system, I would suggest adding some realism by making waiting times longer the more hurt you are. Not by a large margin, but someone near death wouldn’t sprint towards the enemy like someone who just entered into battle with full health.
Lately FF games have been making it easier and easier for people to play, entire actions brought back to single button, so it seems that you are playing a Dynasty warriors game. The thing that separated FF gamers is that they took the time to learn a somewhat hard system, which made the entire game all the more enjoyable. Button bashing, or in FFXII case, not pushing buttons at all, is not what Final fantasy is about.
Instead of bringing the old games back to life, let's make the new ones worth playing.