And what's wrong with Locke? He's my favorite character from VI. The only problem I can see with him being in Dissidia is that he and Zidane are very much alike. And if Faris was in Dissidia (I hope not, D'yar, and doubt it, as they're already following a trend of main character/main villain) she'd prolly have blonde hair, as Dissidia models are based off Amano art, in which Faris had blond hair. The spriters felt this didn't work (prolly cuz Krile also had blond hair) and changed it.
And it can't be Locke anyway, as Kefka mentioned a special friend of his that was a girl, so either Terra or Celes. I am hoping for Celes, but it'd be more likely for Terra to appear.