I feel like "single shared namespace" works best when the ecosystem is managed collaboratively, with a clear leadership to make calls on who gets what name— for example, something like a Linux distro, where there are Replaces/Provides metadata specifically to facilitate these kinds of transitions and avoid being stuck forever with crappy legacy nonsense.

But this doesn't work at all in a free-for-all environment like PyPI, NPM, or Crates, where anyone can just grab a name and then have it in perpetuity.

IMO the Docker ecosystem got this right, with baking in a domain name as part of the container, and insisting that everyone on docker.io use a vendor/product convention. This meant that the toplevel namespace was reserved for them to offer (or delegate the offering of) specific blessed container images, much more in line with how distro packaging might work.

    # Get the "official" image, whatever that means (but you trust Docker Inc, so yay).
    docker pull nginx

    # Get an image supplied by a specific vendor.
    docker pull bitnami/nginx

    # Get an image from a different server altogether; maybe it's your company, or you don't trust Docker Inc after all?
    docker pull quay.io/jitesoft/nginx

Maybe the big-flat-namespace thing is still a years-later reaction against huge and unnecessary hierarchies in Java land? I think the ideal is not to permit infinite depth, but perhaps to insist on 2-3 levels.