Noncompliance and legality are 2 very different realms.
Let's just be clear. They are enforcing 1934 and 1968. They did enforce the Clinton ban. They are currently enforcing CA, MA, CO, NY restrictions including magazine restrictions. They are enforcing "destructive device" laws. They are enforcing the SBR and silencer tax stamps. They enforce serial laws.
But oh, oh this one law will be a bridge too far. Hasn't been in California... I'll do the proper British thing and bring you a pint of ale on your way up Clink Street.
I'll even go so far as to say the 2nd Amendment clearly states you have the right to an unregistered supressed short barrel machine gun. Just doesn't work that way in practice.