Well, there was a tweet from a Warner Bros. employee, but now it's gone. But before it was taken down, there was a screenshot of the roster selection screen for Injustice: Gods Among Us
Two characters are now confirmed that haven't been announced yet before. First up is Ares. Now, if you are reading the awesome comic book, and you should be, you know he makes an appearance to talk with Superman and Wonder Woman. So his inclusion on the game isn't that much of a surprise.
Killer Frost has yet to show up in the comic so she's new and one that I'm interested to see how she's involved in all of this. Hopefully, we'll get a few videos soon to show off what she and Ares can do.