Nothing is confirmed, but I'd love to see it happen
Recently in a blog post from Capcom producer Tomoaki Ayano, a number of Ultra Street Fighter IV-related questions were touched upon in addition to the re-iteration of the absence of "effect taunts." (Say goodbye to a possible Rolento grenade taunt.) Most notably, the lack of support for two very popular franchise characters, Alex and Karin, was brought up. When asked why Alex wasn't added to the Ultra roster (although he is rumored to be), Ayano stated, "Being the main character of Street Fighter 3 and all, Alex sure is popular, isn't he? Having both strong normal attacks and good throws, he certainly seems like he'd be a strong character."
Karin was also mentioned, to which Ayano responded curiously, "She got 1st place in the national popularity poll, didn't she? Personally, there are a lot of character I'd want to add to Ultra Street Fighter 4, but please look forward to further announcements!" While this isn't confirmation, it's nice to see that anything is being considered, and with major fan input being considered for all things Ultra related, a character as popular as Karin could easily make it into the game at some point.
Perhaps he's saving them for an Ultra Street Fighter IV Turbo on PS4 and Xbox One?