I’m like the only one here who highly doubts it will be Asura. Capcom may be lazy but they wont transplant a character from another game universe into an official entry in an SF game unless they are planning to fold the two universes together.
I think it’s most likely going to be another Final Fight character. Given the fact that 3 out of 4 of the characters being ported over have their origins in Final Fight (Poison/Hugo/Rolento) it would make sense to bring Haggar over. However on the flip side, Haggar shares a number of moves with Zangief (specifically SPD/Lariat which are moves canonically Zangief learned from Haggar’s days in Saturday Night Slam Masters), plus Capcom is moving Hugo over who is a grappler already which somewhat weakens Haggar’s chances.
It would be cool if Haggar is in as it would be the first time since the original Fight Fight that all 3 of the original FF cast have appeared together in the same game (Cody/Haggar/Guy) (not counting spin-off/ports like Final Fight One or Mighty Final Fight which are still basically the original FF but with a twist)
Spoiler
http://www.destructoid.com/elephant/ul/5892-468x-mike_haggar.jpg
Maki seems POSSIBLE. She was heavily requested on the forums and received 9.3% of the votes from Japan in the popularity contest (putting her at #20 out of like 60something). The statement that the character has “never been in an SF game before” really hurts her chances though. She has been in CvS2 (not an SF but heavily SF based) and more damning she was somewhat obscurely put into the SF Alpha 3 MAX PSP Port meaning she has technically been in an SF game but I’m not sure that they count that one somewhat unpopular port.
I’d actually like Maki, but if they do include her I hope that they further emphasize her differences from Guy and really make her shine as her own character even more.
Spoiler
http://images2.wikia.nocookie.net/__cb20100105132246/streetfighter/images/3/3c/FileSFA3Maki.png
Lucia seems like a nice surprise character if they don’t go with Maki. She has never been in an SF game but she has appeared in some endings and such. It’d be interesting to see how they expand on her move set but she has some interesting stuff that doesn’t resemble much of anyone elses in SF. (Including a kick that looks alot like Terry Bogard’s “Crack Shoot”)
Spoiler
http://spritedatabase.net/files/snes/406/Sprite/FF3_Lucia.gif
If they wanted to troll they could bring in the official Street Fighter karate clown: Philippe, who was a boss in Final Fight 2.
Spoiler
http://fightingstreet.com/folders/artworkfolder/artworkpics/ff_art/ff2_art/ff2_fullbodyart/ff2_fullbody_philippe.jpg
Gou Hibiki (Dan’s Dad) is def a strong possibility. TBH not who I’d pick but I think he has a decent shot, though they’d have to pull the “I wasn’t dead, I was just resting.” card out again like they did with Gouken, since Sagat killed Gou.
Spoiler
http://imagenes.levelup.com/uploads/news/photos/news_photo_1245427689.jpg
Of course there is also the possibility that they could finally do what a lot of people thought already happened and fold the Rival Schools universe into the Street Fighter universe and bring over Batsu or Akira or someone else. Technically Sakura’s appearance in Rival Schools is non-canon for storyline reasons and is considered a guest character, but they could make RS part of the SF universe conceivably.
Spoiler
http://t3.gstatic.com/images?q=tbn:ANd9GcT6HXXZlQ72JMdxRioWiED7oPoewS0Do6AA0h24hyFwWFHoXkxPOQ
At least these are some of my guesses.