Is your feature request related to a problem? Please describe.

I am working on updating sphinx and sphinxcontrib packages in nixpkgs, which has its own quirks in its method for Python packaging. I don't fully understand why, but mixing packages that use setuptool's legacy namespace packages with those that use implicit namespace packages (e.g. sphinxcontrib-jquery, sphinxcontrib-applehelp) cause the latter to be considered missing when importing them.

I cannot reproduce this in a virtualenv, so it could be Nix specific, but it's also strange enough that I fear sinking tons of time into it if there's already a plan to migrate and release all the sphinxcontrib packages using either setuptools's or flit's support for implicit namespace packages. I am also willing to help with testing, PRs, or in any other way.