+1 for this approach (and thanks for all your work on PyPI William!).
FWIW, I think it's worth clarifying that PyPI is already involved in malware detection and takedowns (as are almost all the package registries). The curation that commercial vendors offer is a little more nuanced than excluding known malware (for example, allowing users to restrict their downloads to a "known good" set of packages, rather than "only" excluding "known bad" ones).