Supposedly majority of the development team are working on versus XIII after finishing XIII-2. But my money is still on XIII-3 to come out first.... likely in 2013.
I'm almost certain and willing to wager that Versus XIII will never come out. If and when it does get released, it'll break Duke Nukem as the most delayed game in history. Even if Versus XIII is on track to be released within the next couple of years, they've been working on this game so long that the game is already going to look dated, and square enix will have to start over with a more current or next gen (PS4?) engine.