This is what a lot of people who were voicing concerns about the bumpstock ban were trying to sound the alarm about. It was never about the product itself, just the ATF, among other individual(s) within the Executive branch, abusing power. First it was about a gimmick product, now it has expanded to laser etched flats of steel, and also slivers of metal.
If they can reclassify a stock, a sliver, or a rectangular piece of metal to be a machinegun; what’s to stop them from reclassifying a muzzle device to be considered a suppressor/silencer? Or reclassifying AOW shotguns to be short barreled shotguns?
Or a 4 oz piece of plastic that they said was legal 4 months ago but, now, changes your weapon into a regulated NFA item, potentially, turning 10-40,000,000 law abiding Americans into felons.