1. There was a discussion few years ago to remove the signatures from the format at all. I don't know what the resolution was, that's why I don't know if it's still supported, as in is it supported by the specification or not.

2. Lock files are hilariously wrong in Python. They don't accomplish what they claim because the only tool that in principle could do that and that is actually used with Python deployment / development is conda, and to the best of my knowledge conda's environment doesn't support locks. All other installers don't even guarantee that successfully running them will produce an environment with all dependencies met. But, not only that, they don't prevent users from becoming victims of manipulations that happen index-side because they don't store the checksums.

3. "nontrivial percent of Python users actually want this behavior." I'm yet to find one. Most Python users simply don't understand how any of their packaging works and come up with absurdly bad ideas and "solutions" to their problems. They may tell you they want something in the same sense as a drug addict may tell you they want more drugs, but the "actually" isn't there. They "actually" don't know what they want most of the time.

> You can’t modify distribution files on PyPI, you can only add new, unique ones.

I just gave an example of how this modifies the package. Not sure what problem do you see with it.