Hi @mboisson! This is a 1.5+ year old discussion that ended with a conclusion to do things a certain way and relevant rollouts have already happened. I think it would be good to not reopen this thread with a new idea.
Note that versions with local version labels are already supposed to be preferred over versions permitted on PyPI.
That said, I also wanna respond to the idea proposed: I don’t think using local version labels as an environment marker works well — their semantics don’t really fit what we want here with missing markers being errors and the marker environment being different based on what choice is made for a different dependency makes this a no-go.
I think the wider consensus is that what we want is proper support for variants of a package based on platform capabilities/ABI etc and how to make that feasible is being discussed in other topics right now. The current discussion has meaningfully moved forward from when this was brought up and is happening over at Selecting variant wheels according to a semi-static specification now (which has links to various related threads in OP).