Only have experience with the Wii U so I'll focus on that one.
- Some kind of universal achievement system that's different from the ones found on other platforms (something less generic). Instead of a bunch of numbers you have a trophy room similar to the one in Smash Bros. Melee. Each game gives you 2-3 trophies, which you can arrange in your room. You can also collect other decorative items for the room, Miiverse and your Mii. Have a list on the wall that keeps track of high scores for games that use them, and a Hall of Fame section where you list your favourite games. Use screenshots and artwork from Miiverse/Art Academy and hang them on the wall as posters or paintings. Have a virtual game collection where you can check stats for every game you've played. And you should obviously be able to share your room with others.
If done right I think it could be a pretty cool feature that is unique and gives developers a ton of freedom in how to utilise it.
- Upscale Wii games
- Increase the VC output tenfold. Add GC titles. Add some kind of subscription service to get access to the whole VC library.
- Add Wii games to the eShop. There's really no reason for Nintendo not to add every game they have, and if they're planning HD re-releases then just give owners the option to upgrade to the new version.
- Combine WiiWare and eShop
