I've been thinking more about the "renaming" vs "numbered versions" for packages, and I'm now leaning more strongly towards a distinct version number—or at least a separate version field, number or otherwise.
It's true that the major version number doesn't convey much, except the vague idea that the authors believe it to be better, or they wouldn't have written it. However, as long as they are unique and you have some easy way to find the "latest" version, it doesn't really matter if they're numbers or not. Commit hashes or code names should work just as well.
However, I think there's a simple security argument in favor of making the version a subfield, to prevent spoofing by malicious or mischievous third parties. Otherwise anyone could claim that their fork was "python-4".
An alternate solution might be to add a "successor" field, so that a package could identify another package as the rightful heir, even if it wasn't developed by the same team. That should make the open-source fork-based community development a little easier. You'd still have to know what the root package was to follow the chain though.