The wii itself is possible. Nintendo is selling tons of wii's right now. Emulating the wii at this time is not possible on the iPod. This is because it has nowhere near enough power to emulate the wii, and the fact that there isn't even a wii emulator for the PC Eh, lets make my entire post bold for emphasis...
No offense Danls92, but this needs to be updated just a little bit. Turbo Grafx 16 and the Commodore 64 are both in the works. While the Sega Genesis is already available.
The DS itself is possible. I own a DS myself. It's just inconceivable for it to work on the iPod touch/iPhone. You'd have to cram 2 screens and just about 10 buttons plus the iPod doesn't have the power to emulate the DS. Yes, I know with the new iControlpad the controls will be easier, but it still needs to actually be emulated.
Just one screen then? (i.e. a game that uses the second screen as a map couldn't be emulated, but if you got rid of the "map" screen surely it would work?)