At a recent Microsoft Gamefest 2008 event in Seattle; Epic's president Mike Capps told the audience that the next version of it's Unreal Engine will be ready when the next-generation of gaming begins. It will be fronted on the Xbox 360
"We've got Unreal [Engine] 4 in production right now... it's going to be in the next console generation - our rough guess is 2012 [to] 2018."
"Version 4 will exclusively target the next console generation, Microsoft's successor for the Xbox 360, Sony's successor for the Playstation 3 - and if Nintendo ships a machine with similar hardware specs, then that also. PCs will follow after that."
[SOURCE]