It's too late now for Wii U.
The audience for third party games is on Sony/MS ... I think Nintendo is just better off going a different route at this point.
In the Fusion setup at least they would have the whole "you can play a real Madden/COD/Resident Evil on the road!" if they go the shared library route, I think third parties might bite on a unified platform. At least for a year or two.