I don't want to see them bringing back a bunch of characters...I want to see all new characters like with SF3. If you HAVE to bring back some old characters, I say do it like this:
Jump the storyline ahead 10 or so years. The new main character is Ken's son, Mel Masters. He plays like a cross between Ryu and Ken. The other shoto to go along with him will be an older and more mature Sakura. Ryu would also be present, taking Gouki's place as a hidden boss character. Give him a bunch of brand new moves. Everyone else will be brand new. They can always go the Remy route and just create new characters with older characters' move sets.
What about the SF3 characters? It's time to bring back Street Fighter Alpha. Alpha 4 would feature the SF3 cast alongside the SFA3 cast, with a few new additions. Throw Maki and Eagle in there, and add Poison and Haggar as playable characters.