I think I was confusing this and another recent (similar) request.
There’s no means of marking a project as deprecated, largely because that would involve PyPI getting into the business of curating packages, which we don’t do. Sure, “this is unmaintained” seems like a relatively uncontroversial statement (assuming due process in establishing it) but once we start down that route, it very soon becomes a significant undertaking. There’s a lot of projects on PyPI that “obviously” aren’t for serious use and/or are unmaintained. For example, what about this project?
I’m not a PyPI maintainer/administrator, so I don’t speak for anyone but myself, but I don’t think it’s sustainable to start down the route of any sort of curation of projects on PyPI at this point. Maybe if we had a significant number of people offering to do the work…?