Respectfully, Lash, I'm not sure I see where you're getting that part. Do you mean this:
1. New Definition of Firearm Frame or Receiver
The proposed definition of this term would maintain current classifications and current marking requirements of firearm frames or receivers, except that the licensed manufacturer or importer must mark on new designs or configurations either: their name or recognized abbreviation), and city and State (or recognized abbreviation) where they maintain their place of business; or their name (or recognized abbreviation) and their abbreviated FFL number, on each part defined as a frame or receiver, along with the serial number. To ensure traceability if the parts are separated, there would no longer be an option only to mark the FFL’s name, city, and state on the slide or barrel. More specifically—
•The proposed definitions would take into account the fact that modern firearms do not house all the components as defined in the current definition. These definitions account for firearms such as split frames or multi-piece firearms;
•The proposed definition would recognize the current classifications of a firearm “frame or receiver.” It is intended to encompass the majority, if not all, of existing regulated firearms, and no new marking requirements would be required for these existing designs and configurations;
•After this proposed rule is finalized, markings on new designs or configurations of firearms manufactured or imported may be accomplished by marking each frame or receiver with the licensee’s name, city, and state, and serial number, or with the licensee’s name and abbreviated license number prefix and number (serial number) in the manner prescribed by existing marking requirements;
•Markings would need to be accomplished within 7 days of completion of the active manufacturing process for the complete weapon (or frame or receiver of such weapon if not being sold as a complete weapon); and
•The proposed rule would require acquisition and disposition record changes to accommodate recording multiple frames or receivers that have different serial numbers if the original frames or receivers (with the same serial number) become separated and are reassembled with frames or receivers bearing different serial numbers
(^ pp. 58, 59, 60)
That's what's being proposed, no? If that's the case and current classifications, as listed in an addendum (and in my earlier post) to the document, clearly show the lower (and just the lower) of an AR-type rifle labeled as the "frame/receiver" (i.e., the firearm), then that doesn't mean they're gonna end up serializing/registering all upper receivers. Unless I'm missing some key point there, and I admit I could be. Seems to me that only "new" designs would require it, and how many new designs that aren't derived from the AR or any of the preexisting classifications are coming out these days? Not saying they won't come out, and I'm not saying this is feel-good anything, but I am saying that I'm not sure I see the same thing here that you're seeing.
The only part, maybe, is the "new configuration" part but I didn't see anywhere they explained it. They do list "alternatives considered" which did include full serializing but that was decided against.
www.atf.gov 
