Hmmm...interesting that the pad has A, B, Start and Z buttons, but no X, Y, L or R. L and R would be hard to implement, because they are analog buttons, but why not X and Y? There's plenty of room for them at the bottom of the pad...they would just have to move the warning messages that no one ever reads to the back of the pad. Oh well.
Do you suppose that the direction arrows correspond to the analog stick directions or to the D-Pad directions? I would guess that the arrows correspond to the D-Pad, since the D-Pad is already digital, but I hope that the arrows correspond to the analog stick. That way, you could use the pad to play other GameCube games! Smash Smash Revolution, anyone? Even without the X, Y, L, R, and D-Up buttons, playing SSBM on a DDR pad would be crazily fun.