Ultra Street Fighter IV has been stirring a lot of musings and guesses ever since they announced, that they weren't going to announce the 5th character. They did however leave Seven clues for fans to ponder upon;
1.) It is a Capcom character.
2.) It isn’t Asura or Bad Box Art Mega Man.
3.) Ultra Street Fighter IV will mark this character’s fighting game debut.
4.) It is a character that isn’t on anyone’s radar.
5.) The character will be a perfect fit for the Street Fighter universe.
6.) The character is a female.
7.) She is in the Street Fighter comics.
Using my superior knowledge of Street Fighter and it's related media, I have made a list of possible candidates. Some are obviously going to be more likely than the others but please bare in mind this list is in no particular order.
Any one of the M.Bison's Dolls (except Juni and Juli)
Juni and Juli were the lucky two given fighting roles in Street Fighter Alpha 3 and the rest were played for cameos. Now this gives another one of the lucky dolls a chance to share the limelight with their superior sister Cammy. Honestly they are all pretty much the same apart from two character traits listed in the wiki, so Capcom could freely choose whichever and no one would suspect it. Although I'm going to guess they will go for Noembelu because she is special enough to get a whole webpage of the wiki dedicated to her.
Teenage Back-Up Girlfriends (Kei Chitose and Sarai Kurosawa)
I was going to have separate entries for each of the girls but they are essentially the same, apart from the leads they follow. Kei Chitose is Sakura's best friend and reluctantly follows her through around the world, being featured in her fight openings and endings. Sarai Kurosawa appears to be more pro-active as after being attacked by Ibuki in Street Fighter III she appears to be training to be a Ninja in Ibuki's Arcade mode ending. Capcom can put either one of these two into the USFIV as a joke character and I'll be happy.
With the many clones of Ryu that have spawned; from Ken to Gouken and from Akuma to Evil Ryu, why not have a clone based off Sakura? She would also fit the criteria listed above; she appears at the end of Ganbaru Sakura, never was considered by anyone since she is already a character in SFIV, female Capcom Character and will be making her fighting game debut. You could even say it was hinted at in the SSIV Sakura ending. Just as a side note; isn't Sakura supposed to be like 20 in the Street Fighter canon when SFIV rolls round??
A Transgendered Woman
We all know that Final Fight's Poison when brought to the West was changed to a cross-dresser because hitting women is bad. But why can't we have a Woman who wants to fight and so dresses as a man? I bring you Wong Who from Final Fight!
How can you say that isn't a woman cross dressing? Look at the long hair, Asian beauty and look at that chest! It's enough to make Ingrid jealous. Wong Who fights for the women who want to be treated as a man in a battle and not be pitied because of their appearance or social etiquette.
She spoke to Elena for a few panels in the Street Fighter Legends: Ibuki comic series. Having a speaking role, name and appearance makes her good enough for Street Fighter.