Lionhead does say that the new unannounced title will be powered by the Unreal Engine 4, so expected with UE3 and UE4 would be nice. The posting does add that while they are using a third party engine, they are developing a significant amount of the graphics technology in house in order to push the abilities of the next-generation of hardware.
Hard to say what Lionhead might be hiring for, but there is good chance it is for a new Fable game perhaps, but we know that there is more than that going on at Lionhead these days so it is anyones guess at the moment.