Check out this neat little article about the WII-U browser gamepad tests
No Audio support
No Web Audio API
No WebGL, WebSockets, or File API
No AppCache, some security
Framerate is very low (~10 FPS for tested games)
Well, I wasn't expecting much more, honestly.
Develop games in your browser. Powerful, performant & highly capable.
The article shows some pretty okay results though.
It's definitely not going to be running any graphics intensive games yet, but imagine the next console in 5 years.
Some people are saying you can get Touch support as well :)