That's very true, unfortunately. As good as the Emerson decision was in light of the court's dicta about the RKBA, even that court left open the door for more, not less, gun control since it left intact the restraining order provision, something that is clearly unconstitutional. Many other Federal District Appellate Courts, like the infamous 9th Circuit, have never rendered a decision that was postive for the RKBA. In fact, the 9th Circuit has consistently found against the RKBA and it searches high and low for obscure, mostly unrelated case law, in order to justify complete government control of who gets guns. In blatant cases, like the 1992 Fresno Rod and Gun Club v. Van de Kamp (then AG for California) they purposefully misused Cruikshank to uphold the unconstitutional Roberti-Roos AW ban. The 9th Circuit is composed of neo-nazis.
IMHO, there was no repeal because the NFA is a revenue raising measure, and as such in and of it'self Constitutional.
There have been other USSC decisons to the effect that revenue laws cannot be promolgated in order to effect social modification.
A $200. tax in order to posses and to even transfer ownership of a 50 dollar weapon could not be seen any other way.
Machine guns could be bought at the time as surplus arms for a mere few dollars, or brought into the country as war souveniers without any cost.