It'll be funny if the GameCube controller will be compatible with the next Nintendo home console. It has to die eventually.
I'm sure not yet for next hardware, assuming that the next hardware will still have multiple USB ports. If Wii U's architecture will be shared to the next home console, then porting the drivers for the Gamecube adapter will be easy for them.
Maybe we'll be surprised to see that the next controller is inspired with the Gamecube controller look.