Neversoft previously posted an announcement that it was looking for programmers for the PlayStation 3, and has now posted a job opening for an Xbox 2 Console Engine Programmer. Given that the person will be responsible for porting the "Neversoft Engine to Xbox2," including "all platform-specific code such as rendering, audio, IO," it wouldn't be much of a surprise if Tony Hawk's Underground was brought over to both the PlayStation 3 and Xbox Next.
News source: GamePro