This has never been done before and you should know that the Wii U does not emulate the Wii it has a Wii "inside it". Therefore I would consider it impossible to accomplish something like this since while an emulator can be made to replace textures, especially for everything post ps1, games running on native hardware would probably not be be able to.
I imagine you'd first need to find a way to let the vWii have access to the extra hardware found in the Wii U, which the only thing we have so far is higher-than-Wii clock speeds for the CPU (which is NOT overclocking btw). For higher resolutioned assets you'd probably need a lot more of the Wii U's extra hardware to be available, one of the many examples being more ram.
The general rule of "if it were easy it would have already been done" applies here. Heck Nintendo could have done it for their vWii titles if it were possible.
Still it is an interesting thought, but unless you are prepared to make it possible yourself then it most likely won't be done since the Wii U does not get much attention and devs working on it are few.
Oh yeah and Dolphin has never been ported to Wii U since there's Gamecube hardware directly inside of it. I'm not even sure how viable Gamecube emulation, let alone Wii emulation, would be on the Wii U.
