Sure it would be possible. See the Dolphin emulator. You just process the 3D assets at a higher granularity, maybe throw in some anti-aliasing... Tah-dah!
But your mileage may vary (3D art assets might come out looking much better, but 2D art assets might just end up looking fuzzy, because they have to be scaled rather than rendered), and it might introduce some compatibility problems. The last one is the killer. You may have noticed that Nintendo backwards compatibility tends to shift the Wii right into Gamecube mode, with no access to the home menu and other Wii features. I haven't really explored 3DS BC much, but it seems to also shift the device into DS firmware mode. It can jump back to 3DS mode without a restart, though.
The point is that Nintendo may opt to ensure that 100% of Wii games work just as well as they did on the original console, rather than add a shiny new paint job which could gum up the works for some games.
"The worst part about these reviews is they are [subjective]--and their scores often depend on how drunk you got the media at a Street Fighter event." — Mona Hamilton, Capcom Senior VP of Marketing
*Image indefinitely borrowed from BrainBoxLtd without his consent.
