I don't really think it matters is the UE4 engine can run on WiiU or not. Either way there will be great games on the system.
But.... If Epic does with UE4 what it did with UE3, then it will be scalable to almost any platform including smart phones & tablets. Epic likes to make a versatile engine that they can sell for use in many areas.
But then again we still don't know what the final spec of the WiiU are....