I would like this. Add Gamecube-games too. It would only be playable in docked mode, as it would be too clunky and needs to much power, but the games it would read were never portable in the first place. WiiU-games using the gamepad might pose a challenge though. Wiimotes should be easily possible to emulate with the Joycons.
I would LOVE to play the original Xenoblade Chronicles, Pandoras Tower, Zack&Wiki and some more on the Switch, even if portable mode is impossible.
For people saying it would cut into profits reselling the games: sure it would. But make it 100€ and you also lose portability in comparison to enhanced ports, so it probably doesn't do too much.