Even if WiiU's GPU will support DX11 features, I still think Nintendo should have gone with more thab a 400-500Gflops GPU. 800Gflops would have been good. 1Tflops would have been perfect.
But now, they won't have multiplateform that push Xbox-PS4.
If they support DX11 then that's realistically all they need for multiplatform support. Porting should be easy and visual quality will be comparable to turning down the settings on a PC game while giving the same essential experience.
The only real questions are whether third parties will even bother with the minimal effort and whether customers will buy if the games are there.