In states that allow MG's it could be legal for civilians to own post '86 guns.
The whole NFA thing deals with interstate transport. So if there is a state law proposed where State residents are allowed to own post '86 MG's if the resident pays the "State ATF" a tax then as long as the guns aren't taken outside of the state they would be legal. The state would have to maintain their own database and would probably make FFL's within the state apply for a State SOT as well.
All it would take is one state to use the State-NFA-item tax to boost monetary support for schools, roads, whatever and the state would se a sizable influx of new residents and a lot more money. The MG world would also be changed up quite a bit.
Think of how nice it would be to go to the gunshop and buy a Lightning Link or RDIAS for a couple hundred rather than a few thousand.