Shizowa san even goes further and tells us to think about who would logically show up after Akuma and we will get a general Idea of who, this mistery character, is. She also adds that we might have only seen this character's shape/profile up until now, ruling out the possibility that this character has been playable before in other Street Fighter game.
I can only think of one character that fits her description and that is Gouken!
Remember that we have already seen his Profile/shape (pictured above) in the SF4 dev blog's april fools post (image enhanced by the guys at www.capcom-town.es)
SPECIAL thanx to Azrael from SRK forums for the translation.
source: SF4 dev blog