We already know that Injustice: Gods Among Us includes comic book royalty like Superman and Batman, but a superhero without his nemesis is just a jerk beating the crap out of poor street thugs. If the game includes B-level characters like Deathstroke, of course it has to feature Lex Luthor and Bane as well.
A scanned issue of @Gamer revealed the pair, and NetherRealm head Ed Boon confirmed it with a tweet. Bane is more styled after his comic book persona than the recent Dark Knight Rises incarnation, for reasons that should be obvious to anyone who watched the movie. Lex, meanwhile, sports his trademark Warsuit, because without a billion dollars in electronics he's just a rich weakling whose fights against superhumans would go something like this.