VERY interesting case.
One who is a bit daring can, I suppose, manufacture a machinegun without bothering to register it or to ask permission.
Then one can claim that since NFA is not applicable, the only bar is the 1986 law, which is patently un-constitutional, as machineguns are most certainly 'military use' weapons, as contemplated and approved under the 2A.
Of course, the first $300K in legal fees are the hard part.
The 3AM raid in which your pregnant wife is beaten into miscarrying and your cat is stomped to death is pretty unsettling too. And the BATFE does those things, though not yet in a single "raid". (Note that the even use the military term for what they do, even though they are allegedly a tax collection agency. )