I would actually very much enjoy having the option.
The thing is... I've got a number of friends who really aren't into the motion controls. Not because they think they're bad, but because they don't have a wii, and arn't used to them. They're only over occasionally, so its not worth it to go "well, learn the controls so we can play" Its just so much easier to play something else instead.
Having GCN controller as an option would be good, even if it meant We'd both have to use GCN controllers to make it fair. However, I don't think it should be an option for online, simply because Online needs to have standards.
Another reason why it would be good is because, well, sometimes I have to move my wii to my room, and the setup there is... Not very good for pointer controls. The TV is small, the seating is awkward, and I have to be really close to the TV. If GCN was an option, I'd totally use it in this situation.
The last argument for gcn is... In big rooms, where 4 people are playing. if you have to use the pointer feature, they can't spread out as much, otherwise people will start being out of the line of sight of the sensor bar.
I guess all those arguments are pretty minor, but hey. Its a pretty minor addition.