The main attack vector IMHO is the simple fact that one can sneak in new packages with malicious intent by simply contributing a new formula. The team of maintainers is too small to audit all of the newly contributed formulae. I'm suprised that this attack vector wasn't part of the audit.
I don’t think the current Homebrew core formulae reviewers consider their team too small to sufficiently review all new incoming formula requests. But even if it was: this is one of the vagaries of packaging that’s explicitly called out in the post: the boundary between first- and third-party execution is inherently murky, and there’s IMO relatively more security “value” in determining where third-party execution can surprisingly happen than pointing out all of the unsurprising things that happen when you intentionally run third-party code.
(With that being said, I think packagaging ecosystems in general should be reviewed for those kinds of acceptance processes. But that would be closer to a “red team” style audit than a software audit, since it’s about human processes.)