From my point of view, it seems like a step backwards to move towards an implementation defined standard again. Are people likely to write a competitor to auditwheel? Well no – although I’ve defintely seen people who wanted to compile the code using their infrastructure and were OK with carefully crafting wheels in order to comply with the PEP-- but I think there is real value in making it so people could. We’ve spent a significant amount of effort, and still have a significant amount of effort left to go, of trying to get out from under the historical weight of implementation defined behavior.
As far as getting people to write the actual PEPs… I think that if Warehouse can start validating uploaded wheels, that is a huge driver for people (particularly companies) to put effort into this rather than just hold onto existing standards. Maybe a better way would be to basically write up a PEP template for new manylinux variations, hell there could even be a small tool that generates one from a auditwheel profile so the extra work is super minimal BUT it makes there be an obvious place to describe changes when something has to be done that is more than just revving some glibc version number.