Nintendo will undoubtedly have accessories to make it slide into a "normal" controller. I dont think its gonna be very wise to try and play the old games with a controller like that, except for NES games which feasably could but that would be uncomfortable holding that sideways I'd think...
i will say what I said about PS3 and the rumors around it...
this can either make them or break them... introducing this new controller...we'll have to see how people accept it...and how they adapt to people's frustration with playing cube games and such.