the gamecube discs are small enough that nintendo could make a portable system based on the discs. how cool would it be to have different games or versions of a game on the same disc for portable systems? like if they put the wind waker on a disc with some of the older zelda games to play on the handheld. i'm sure this has been thought of before anyway...
What would be cool is if they could somehow make games that linked with the DS for the GameCube and used it or if the DS could play graphically superior versions of multiplayer GBA games (like a better looking or 3-D version of the Mario Bros. Multiplayer game that every Mario game has) and could link with the regular GBA versions.
Either way, I'm excited to see what Sony and Nintendo finally pull off.