You cannot say that "nothing happens" if they rule against machineguns. Depending on the ruling it could spell confiscation for those who legally own them now or at the very least it puts NFA items on congresses radar and they could decide to raise the transfer tax (set at $200 back in 1934) to a modern equivalent (would be over $3000 today). We all know that Obama loves raising taxes and there would probably be zero oppossion to this from congress. Maybe you do not own any NFA weapons, so you might not care what happens to other NFA owners, but I do.
there's nothing stopping them from doing that right now anyway. Basically what your saying is "ssshhhhh...don't stir the pot and hope no one notices"