We support all Python versions that are not EOL, so we’d do the same as with other features added in newer Pythons: add a # do X when >= 3.14 comment to start using it once it’s available for us. If that’s not required because pip provides a newer parser, that would make me happy if it was for a feature that is much nicer than the 1.0 way.
I’d be fine treating this as any other Python feature: the newest features are available in the newest versions, and it’s up to a project to decided how many older versions to support. That doesn’t require files or parsers to add any version argument complexity, it just requires waiting.