This kinda falls into how I think of the PSvita TV :/ it would be an economy console. Cheap to get, use, and pick up games for. It is a good idea, but the way to go around it for the 3DS is just awkward. Going the economy console route though, either company could end up like sega >_> still producing way old units, well after their prime.
Now linking it with the wii u? That is a balls idea, like the gameboy player or Super gameboy. Something separate would work fine if they could find a way to do it.