Ps all stars will have additional characters.
Until now ( I think) there was only rumors and comments from Omar saying "It's being considered"
http://www.examiner.com/article/superbot-discusses-playstation-all-stars-battle-royale-dlc-characters-stages
But im pretty sure everyone was expecting there to be additional characters, it's just good to finally see someone from superbot confirm it.
Hope its Cloud :P (bet it will end up being kat lol)