How Could Nintendo Improve Upon SMG

[L.C.E.C.]

Make power-ups old-style (Stay until hit)
FULL Co-op (Not P2 can shoot too)
VS. Mini games like in NSMB
Separation of Wiimote and Nunchuk (Shaking either did the same)
New moves (possibly in line with Separation of Wiimote and Nunchuk)