Guerrilla Cambridge, a branch of Killzone studio Guerrilla Games, may have revealed the nature of its upcoming project, as a listing for a job at the studio states that the new hire will get to work on a major existing franchise.
The job listing for this audio programmer position (discovered by NeoGAF) states the individual will contribute to "forthcoming projects in a high profile, multi-million selling franchise." No other information is provided that could identify what franchise this is, but given the studio's history, Killzone is the most obvious candidate.
The Sony-owned Guerrilla Games has long been the developer responsible for the Killzone series. The studio doing the hiring--Guerrilla's UK branch, Guerrilla Cambridge--most recently developed Vita game Killzone: Mercenary (pictured above). Prior to assuming the Guerrilla name, the studio was known as SCE Cambridge Studio and was responsible for the MediEvil games, as well as the disappointing 24: The Game for PlayStation 2.