No way the Switch could emulate the wii u, Zelda BOTW only runs marginally better on the Switch. It needs a lot more cpu power to emulate a different CPU architecture and the Switch doesn't have the 32MB of edram etc. Lack of Gamepad. Any sort of wii u emulation isn't possible. wii emulation is possible of course but that would only need a dvd reader and you can emulate that already on low end systems elsewhere without problems.
I'm sure when the Switch is hacked and has a lot of homebrew we will see gamecube and wii emulators that read iso's from a external hard drive. Nintendo are much more interested in reselling old titles than allowing people to make use of their older bought software. If Nintendo needed something to get the Switch to appeal to more people they might consider it but considering how its selling they don't.