UI on PyPI doesn’t need to be in the PEP, or in any PEP (unless they prefer it to be).
It doesn’t seem difficult to have a long description that says “Don’t use this package, use <href=“this one”>”. Users will figure that out, and it gives the projects far more flexibility than restricting their UI options by hiding things.
That said, I would love to see PyPI be searchable/groupable by the name of the top level module(s) that will be installed. Under such a system, I’d expect this model to get grouped together, along with any other alternative implementations of the same top level module.