From a 2A standpoint, I think the government should simply stand down on 3D printed guns.
They don't get involved when people 3D print a replacement part for...say...their motorcycle, do they? If anyone gets involved there, it would be the motorcycle manufacturer, because someone just took from their revenue stream. If anything, the firearm industry itself needs to go after "outlaw" 3D stuff, because it doesn't have to adhere to the same regulations (sales restrictions, serial numbering, record keeping, etc) as their products do.
People need to quit expecting the government to fix everything. That isn't what "government" is for.