Leon, Xande, Kain/Tifa (already confirmed), Edge/Shadow/Yuffie (I'm obessed with ninja/thieves), Vincent, Zell (could we give his outfits to Tifa?), Kiros, Seifer (give Squall his outfit?), Laguna (just give Squall his outfit), Rinoa (give Tifa her outfit?), Irvine (give Vincent his outfit... lol), Balthier...
Kimahri (we need a bestial hero, I wonder how Red XIII would work), Dressphere Yuna/Paine, Shuyin (an outfit for Tidus), Brother, Yojimbo (an outfit for Jecht?), Auron (give Jecht his outfit).
I still want to play as Blank and also Gilgamesh from 9. Maybe give Zidane an outfit matching Blanc's.

Cameos:
Master Zangan (VII)