Not only is this letter inconsistent with ATFs definition of a pistol, but it also goes against ATFs long standing policy that once a receiver is classified as a certain type of weapon, it remains that type of weapon, even if it has been permanently modified. "Once a machine gun, always a machine gun".
The "logic" here is like saying that if a man puts on a dress he's a woman, and taking it off is a sex change operation.
I am also curious as to how the SCOTUS ruling can apply only to the Thompson Contender, but not anything else. Does each individual model of pistol have to be blessed by SCOTUS?