Price will come down, quality will come up. The first VHS/Beta machines were north of $2000.00, a color printer, 1000.00. So what if a printed AR15 lower will only last a couple hundred rounds. You print off another one and swap it out.
A vhs or printer is not the same as a quality 3D printer or CNC machine. An ink printer is not meant to produce sturdy products, and a vhs doesn't even print anything. A $10,000+ CNC machine will not come down in price to $2k or even $500 where your average joe can afford to buy one.
I think that is beside the point anyway. The issue is making durable products that will last more than just a few rounds. Even more important is that barrels, slides, and springs need to be made from steel or aluminum--not plastic or polymer. I would not want to have to replace a broken gun/part every few rounds anyway; that is just not reasonable
As far as the benefits of 3D printing goes, they are probably limited to magazines and lower receivers only.