You're still going to require specialty gunsmithing tools to ream a barrel, cut rifling, and chamber it. Not to mention threading or pinning a barrel to a frame or receiver. So far you could make the lower receiver to some guns like an AR-15 as it's not a stressed component of the overall rifle.
There is no need to regulate it, nor is it anything "new". Maybe draconian thug countries and states like the U.K., Australia, California in the U.S., etc may try regulating it, but it would only be more feel good bull ****. It's legal to make your own firearm in the U.S. so long as it complies with normal ATF regs or you have the appropriate licenses for manufacturing NFA items. Any respectable gunsmith or machinist can put together a gun from scratch using common smithing tools.
Yes it's possible, no there is no need to regulate the right of the people to keep and bear arms, and yes, **** like this has been steadily advancing for centuries now.