Linking the thread for others’ reference:
I [posted about it over there:
But for others’ reference, current thinking appears to be leaning toward just documenting that upper bounds shouldn’t be used and having them generate a warning, which doesn’t help this scenario at all and if anything is somewhat worse. If --only-binary is made the default and we don’t want a warning every time users try to install the package (not to mention attempting to backtrack through every version, which is already the case, and get the requires-python metadata correct from the start), then it seems we don’t have any real options here than either break all current users or live with this problem forever.
By contrast, Option 2 there would be close to the perfect fix for new backported packages over time, as all it would require is a post-release of the most recent release with a requires-python upper bound to produce the same result as our sdist solution (aside from a not quite as nice error message), except cleaner, simpler and compatible with --only-binary and non-Setuptools build backends.