Unlike the pistol brace ruling, the 80% ban wouldn't be totally retroactive.Here's the million dollar question: What will this proposal accomplish, except to allow the ATF to go after a bunch of innocent gun owners?
Answer: Nothing.
"The ATF calls these firearms privately manufactured firearms (PFM). The ones currently in the hands of the public would not require a serial number unless the firearm is transferred by a federal firearms licensee (FFL) or brought into a gunsmith for work."