This whole discussion feels like trying to overcomplicate something that’s already not a simple to solve a problem that I don’t think is really that widespread. My estimation is that 99% of people who are currently using ``==`` will just immediately switch over to using whatever flag we provide that allows them to still do that. Adding a “do the thing I asked for” detritus to the project seems like a bad idea.
It’s not really any different than if a project say, only released Wheels. While we want to encourage projects to release sdists (and to not ping versions) trying to enforce that isn’t worth the cost. Like most packaging issues, I think that it’s best solved by opening up issues on the offending project’s issue tracker.