Will 480p, you can actually do 8 on the screen at once, but it could be all shared. It might even be Tetris style where they just make it really tiny. Heck, DDR is 4 players now at least on XBox it is. Bluetooth does support up to 7 devices, but then, you can use both GCN and Wiimotes at the same time. You can even use the Wii Classic and the Wiimote at the same time. How do I know all this? Mess around with some Virtual Console games, and you'll find out that now Zelda can be co-op: one person on the B and A and the other on the D-pad on two different controllers. It could lead to more fun the you originally intended. Too add to that, even TP can be done co-op if you split the Wiimote and Nunchuck between 2 people. It's really fun that way even.
Back on the subject though, they could use the Nunchuck and the Wiimote because both feature the tilt functionality. I'd stick with that one because it says it uses the innvation of the Wiimote in some way meaning GCN controllers will not be used unless they designed it like a Mario Kart: DD style where one person is doing something and the other something else like a backup of sorts. This actually makes me wanna see another G&W Gallery game, but on Wii.
[EDIT]: I just realized something, Nintendo can always release a Bluetooth adapter that works via USB to add the ability to have more players at once right?
For any of you that don't know this, the Sega Saturn could support up to 12 players at once and Saturn Bomberman (USA) supported 10 players at once and it would switch into widescreen to do so, but you'd lose certain items. To preserve gameplay, you'd only use one multitap, and you could then use 7 players at once. Lemme tell you, the more players, the better. Think of Mario Party w/ 6 to 8 players. 8 might be too many, but 5 or 6 would really add a lot to it, you can do so much more with that number. Mario Strikers (3 on 3) could actually have 6 people playing at once which is more fun then just having 4. It's especially better to add more players these days when TVs are becoming so large. I've had my 50" big screen for 10+ years now and while it's not HD, that doesn't mean you can't play 8 player games just fine on it (which I have done).