This game already has three per character, but with the way fighters tend to go I think they could add more if they really wanted to milk it.
I would absolutely love to have Sly's tux disguise from Sly 2. Heihachi's hakama would be cool, so would TM2 Sweet Tooth. Either classic Dante or the Neo costume from DmC for Donte? NAKED MGS2 RAIDEN?!?!
RIP CM Punk's credibility, murdered by The Rock. 2002-2013. Not changing this sig until Kanji becomes viable in P4 Arena(started 8/21/2012)