hecterrific said in an interview that the menus seen in the demos were all placeholders including the character select screen. He also said that they hadn't even revealed half the roster, and this was at a time when there were 12 confirmed characters.
Interesting, thanks for the info.
Looking at the selection screen, the lay out etc, I would hazard a guess that additional slots will be added as rows at the bottom, not collums, with possibly another 3 slots on each side.
This would give us 30 Characters, meaning we could have another 6 characters we aren't aware of yet, and of course the mystery Female/Unknown.
6 more characters would be fantastic.