If we put aside the case of building a sdist that is known to fail on the target interpreter, are there any other use cases for this proposal? I can’t think of any, to be honest.
And as far as sdists are concerned, this sounds like something that would be better handled using PEP 725, in particular the external.build-requires and/or external.host-requires fields in pyproject.toml, combined with a DepURL which can identify the Python implementation available in the build/host environment.
At a minimum, I suggest that you take your use case(s) to the PEP 725 discussion thread (which admittedly has been idle for a while), and explore there whether they can be handled with that proposal. If not, you can come back to this proposal with a much better argument for why you need specific metadata just to cover the target implementation.