In my lizard brain opinion, the current fight is what governmental actions trigger 2A protections. And, if 2A protections are triggered, what is the proper level of scrutiny for evaluating the governmental action.
It was in either Heller or McDonald that SCOTUS answered this. Strict scrutiny as keeping and bearing arms is a fundamental right.
Miller would have won his case had his lawyer said "Gentlemen of the court I introduce to you the standard Infantry Trench shotgun, My client is innocent as less than 18 inch barrels are endemic to the Infantry squad." but Miller died and the case was dismissed.
Miller was a no show for the arguments before SCOTUS. His conviction had already been overturned, he was free and clear. Nor did any attorney present any arguments against the government's appeal of the decision of the Appeals Court that overturned that conviction. Only one side was heard, that of the government which had just erected in 1934 a bureaucratic scheme to tax and regulate short barreled shotguns and rifles and fully automatic firearms. Of course they would neglect to mention trench shotguns. By 1939, those weapons were no longer in common use by the general public despite their common use in military services. The consensus in Congress then was that they didn't have the power to criminalize possession due to 2A, but they could tax. They chose $200 because they felt that the vast majority wouldn't be able to afford it in 1934 (still during the Depression). This gave the opening to Scalia to say that only arms in common use are protected and not those that are unusual or dangerous.
This is how we got here!
Strict scrutiny means short barreled, full auto and artillery!