If you've been around the internet, or youtube, you've probably seen this character select screen of Super Street Fighter IV. One thing that should stand out to you, is that there are still 4 slots to be filled. There's already speculation out there that suggests they will be three Street Fighter III characters, and likely one more all-new character. Looking at the layout of the character select screen, you can see why that speculation is pretty concrete.
In one area (left side) you have: Ryu, Ken, Honda, Juri, Chun Li, Dhalsim, Guile, Blanka, and Zangief. That's one new character (Juri), and eight World Warrior (Classic) Street Fighters. To the right of them, we can see three unfilled slots, and in one area we have: Abel, C.Viper, El Fuerte, and Rufus. These characters are the new additions from Street Fighter IV, if you noticed. Next to them, we have the bosses, or Shadoloo team: Bison, Vega, Sagat and Balrog. To their right you see the additions from SF II Turbo: Cammy, Fei Long, Dee Jay, and T.Hawk. Above them you have those crazy a-hole bosses that you hate: Akuma, Seth, and Gouken. Finally, on the far right you have your Street Fighter Alpha characters: Gen, Dan, Sakura, Cody, Guy, Adon, and Rose.
So how does that point to any Street Fighter III characters and one new addition? Well, it's the only game from the Street Fighter series left - besides Street Fighter EX. If you're even thinking Street Fighter EX, don't; most of the newer Street Fighter EX characters I believe are licensed to Akira anyways. Unless Capcom wants to pay them licensing fees for those characters, they'd best go with their own creations. - I'm speaking about Street Fighter III. I anticipate the following characters will make it from Street Fighter III: Makoto, Dudley, and Ibuki. As for the new character? I haven't the slightest idea, but it should be very interesting and fun to see.
Easily my favorite character from Street Fighter III, Makoto.