Two questions:

1. Does this mean it’s a little disingenuous for the Homebrew maintainers to claim that this change has anything to do with app signing, given that they reference the impossibility of unsigned applications in the issue?

2. Does this mean that if a developer self-signs their app but doesn’t notarize it that it will meet Homebrew’s criteria of “passing Gatekeeper checks”?

1. Yes. (Either that or they know something we don't about Apple's future plans.) 2. No, as Gatekeeper checks both for a valid signature from an Apple Developer Program certificate as well as notarization.