This, indeed.
@Dominator211 : I've got plenty of actual wii and gamecube games packed as "wiiu games" and installed using that thread. When starting the game, it asks whether you want to display your game on the gamepad, the television or both. If the game supports
traditional controls (and/or gamecube controls, but I'm not 100% sure of that), you can even play it all the way with the wiiu gamepad. For gamecube games: you can just play all of these with the gamepad.
When closing the game, the wiiu resets itself to the main wiiu menu.
So in the end, it's already perfectly possible and doable. It may be a bit confusing at first, but it's really not hard. In the end, only two small problems might remain:
1) you'll need images to use with the installer to act as banners; while the far majority can easily be found (including all GC ones), it's not 100% yet. You can find what's available
here.
2) there's an upper limit of about 290 channels. It's pretty hard to reach this with just wiiu games (unless you install all sorts of shovelware), but not as much if you also install a whole bunch of favorite wii and gamecube games next to it.