The Wii and the Wii U have the same architecture
Only the CPU is of the same architecture. The GPU in the Wii U, on the other hand, is completely different from the Wii's GPU. Games on the Wii could only go up to 480p, and therefore, were designed with that as the hard-limit. GC games on the Wii didn't use anything extra that the Wii provided because they weren't designed with those in mind. Even PS2 games on the PS3 did not take advantage of the PS3 hardware except for the idea already brought forth about scaling up the final render with filters.
Yes, that all goes without saying, but Wii games on the Wii U will not use the Wii's GPU because it doesn't exist in the Wii U. Therefore, some kind of compatibility layer will be required, so I don't see how scaling or a resolution increase wouldn't be possible. You can't say that Wii and GC games can only output graphics at 480p because that's the hard limit when Dolphin is able to render at higher resolutions (1080p with nice smooth AA), it does this because of how it emulates calls made to the GPU, right?
The only real argument I'm making here, really, is that what people are asking for in this thread isn't impossible ― though I fully understand why Nintendo wouldn't ever implement it. PS2/PS3 isn't the same thing as Wii/WiiU or even GC/Wii. Initially, the PS3 contained PS2 hardware and still managed to apply scaling and filters to games, though subsequent revisions used software for emulation. Scaling didn't look too good, IMO ― but it was possible to disable it.