I wanted to announce that the PEP has been rejected (@pf_moore messaged me privately about it). The reason for the rejection is the lack of sdist support was seemingly enough to cause a lukewarm reception overall to the PEP. I am now going to go think about what an opinionated lock file would look like from me and consider implementing it as part of my mousebender project.
Thanks to everyone who provided feedback! Thanks to @frostming @sdispater for providing early feedback. Extra thanks to @frostming for writing a proof-of-concept locker. And a special thanks to my co-authors, @pradyunsg and @uranusjr .