TimeSplitters 4, but won't confirm anything until after Crysis 2 is released.
CEO Cevat Yerli told CVG, "Yeah, we have been discussing it, but nothing has been confirmed yet, so let's see after Crysis 2."
Free Radical had been starting development on TimeSplitters 4 in 2006, not long after TimeSplitters: Future Perfect was released for last-gen systems, the PlayStation 2, Xbox and GameCube. However, the studio went into administration in 2008, but was purchased by Crytek and renamed Crytek UK. Crytek UK is currently responsible for the multiplayer portion of Crysis 2.
It is entirely possible that TimeSplitters 4 will be Crytek's next game, as the popular IP has been unused for far too long.