Pretty much the same thing most people want. Less linearity.
Two or three costume changes for characters would be fantastic. Nothing off the wall and completely ridiculous (I'm lookin' atchu Summoner Serah).
Airships definitely need to return in some format. Even the ability to customize the airship a little - speed/playable airship battles maybe. Would be a first for Final Fantasy.
Magic needs to stay the same with new effects of course.
And the big one for me anyhow is to have a REALLY great cast. So far the playable characters in this game seem very dark and moody. We need some characters a little lighter and with a more carefree attitude.
Also, finally show Etro and I mean really show her if she's a part of this game.