Looks like a third Street Fighter game for mobile is in the works. The new game is Street Fighter IV Arena, and Capcom's working on it with Nexon, with a planned beta test in Korea later this year.
While few details are available beyond that - and my Korean is a bit rusty and/or non-existent, it's easy to speculate that this could be a free-to-play game given that Nexon makes those and that Korea is huge on free-to-play. As well, with Ultra Street Fighter IV making its way out, we can hope for some new fighters, though whether this one even makes its way to the US is a good question indeed.
Street Fighter IV Arena Upcoming AppWatch Button Watch App