Asura is a good guess for the 5th character but Ono said it's not possibru: http://www.eventhubs.com/news/2013/jul/14/ono-rules-out-asura-bad-box-art-mega-man-5th-street-fighter-4-character-talking-evo-players-about-game-balance/
And I'm really exited for this update. I've had every street fighter from Plain Street Fighter 4 to Super Street Fighter Arcade Edition 2012. It's the best fighting game this generation and I play it all the time still. Also there's a 2014 patch coming up that will change every character in the roster- so it'll feel like a completely new game.