Yeah, I’d vote for using the environment variable to point at a JSON file containing the info (and possibly there’s alignment here with PEP 739?).
I would also very much like a way to override the platform tag that packaging chooses for the current system. I’d love to be able to embed a configuration file in a Python environment that says “instead of win32, pretend this is my_special_platform” (and then point at a private package index to get perfectly matched custom builds). If you’re going to go for a big change here, please keep going 