A five figure CNC mill is capable of making AR lowers. And a few grand of shop equipment is sufficient to finish 80% lowers.
I have a business idea for an Adult Build A Bear Workshop. You roll in to the store, which is in a shopping mall or similar. You pick out an 80% lower and get it laser engraved with a custom rollmark at the laser engraving station, then you take it to a CNC drill press and push the button to finish it yourself. Then, just like accessorizing your stuffed animal at Build-A-Bear, you get to dress up your AR with bins of different types of stocks, handguards, uppers, etc.
It is perfectly legal to manufacture your own firearm, no serial number or background check required, so long as it is for personal use. ATF has grudgingly said that pushing the "START" button on a CNC machine counts as being the manufacturer. I think it'd be a great idea for a business. Walk into the mall, walk out in a few hours with a custom AR-15, no 4473, no serial number.
3D printers and cheaper CNC technology mean that any hope of enforcing gun control is a fantasy, too. It is already possible to make simple AK-pattern rifles with crude tools (Pakistani goat herders do it all the time, and there's internet photos of a guy that made an AK out of a shovel...), but I'm sure Americans can figure out how to make higher quality AR-pattern rifles at home. I know the cartels that brew up meth and smuggle in tons of cocaine will figure it out if they need to.