There is a man at capandball.eu who shoots a variety of WW2 sub guns that have been converted to fire semiauto only. The outward appearance is unchanged and they still fire from an open bolt so if SBR was overturned the Antis would still wet their pants from looks alone.
The whole 1934 law was hysteria from Hollywood gangster movies, there was no real problem.
A few comments on the good point you make.
The major selling points for NFA were Prohibition gangsters, and ,so called "Automobile bandits". Neither issue had any direct connection with guns beyond being tools, both were equally, maybe more dependent on the automobile than the fire arm, and both issues went away when the true issues were addressed. Gangsters quit having beer wars when the ridiculous and unenforceable "Prohibition" was repealed, and the reign of terror of the likes of Dillinger and Pretty Boy Floyd was brought under control by expanding cooperation between police jurisdictions and the expansion of the FBI into a "National Police Force"
At that point the NFA no longer served any useful purpose EXCEPT, It was a TAX thought up by the Dems.