Since the motors are engaged full time (no freewheel) and are self-exciting, they're going to give some drag due to iron losses, which is magnified by the geari

Since the motors are engaged full time (no freewheel) and are self-exciting, they're going to give some drag due to iron losses, which is magnified by the gearing of the belts, as well as some stored angular momentum. So I think it could work as a non-powered board, but not very well.