So far it seems efforts to expand the federal now renewed Undetectable Firearms Act (UFA) have settled for the moment. However the biggest threats still exists at the state level, such as California's SB808 "Ghost Gun" bill that would require DOJ authorization prior to making any firearm by an unlicensed individual, along with a long list of logistical requirements on top of a fee and the possibility of your house being subject to random searches if you chose to comply. As currently written SB808 applies to 3D printed firearms but also so called "80% Lowers" sold by various manufactures.
If passed as amended SB808 would require all parts legally defined as "firearms" such as AR lowers bear a serial number issued by the DOJ by 1-1-2016, and no new firearms may be made without permission. Firearms certified under "Curio and Relic (C&R)" status are exempt. Realistically, the law itself is almost entirely unenforceable and only criminalizes law abiding citizens.