I would totally play this game. My two favorite video game companies ever joining forces once again! The inclusion of Geno is a nice touch. I'd also like to see some more FF characters replace the summons (Terra or Locke or Balthier maybe). In fact, just replace your Final Fantasy section with these characters:

Final Fantasy
Cloud (Original, KH, and AC costumes)
Sephiroth (Original, KH, and shirtless costumes)
Zidane Vivi (screw monkey boy, plus Vivi is better than generic black mage)
Beatrix Gilgamesh
Shiva Terra
Bahamut Balthier
Black Mage Rikku (girl power)
Kefka
Yang
ChFrocobo (with Sazh too I guess)