I like the first party roster, but wouldn't mind seeing characters like Dart Feld, Rudy Roughknight or Joel & Ellie.
The third party roster... switch out Donte with Lara Croft and we're good.
As for stages, I could really go for a Gravity Rush X Journey stage. Kinda like the one they had planned:
Stages were interesting and creative. Mash-ups brought some new takes on stages. DLC stages were the best hands down though. They blew away every other stage in the game.