I don’t get the concern here. 3D printing files are essentially CNC files, they are not any kind of “special” files. In some 30 years of CNC use I haven’t seen a “Napster” for CNC files yet, have you? Despite some of them describing production operations of some expensive parts.
Additionally, it’s a bit too late to get your panties in a bunch over (illegal) 3D model sharing – 3D models as well as any kind of file imaginable are probably shared just as much as any other file type over peer-to-peer connections and have been for ages now (10 years easily). Perhaps not specifically for 3D printing but for 3D rendering.
There’s already a “Napster” or “Napsters” for legal 3D file sharing – Thingiverse obviously and Shapeways list of publicly shared models. What exactly should “illegal” 3D printer “Napster” do to justify the wrath of the “3D manufacturing lobby” – a comment made tongue in cheek, obviously because 3D manufacturing has not and will not have a clout strong enough and unified enough to create a lobby anywhere close to that MPAA was able to field. Besides, profits in 3D printing/manufacturing are nowhere near ones that provide (comfortable) livelihood for the army of MPAA lawyers. I don’t see 3D printing DRM materialize anywhere in the foreseen future.
So, I call the concept of 3D printing piracy a “manufactured controversy”