While I have no strong opinions about the details of whatever mechanisms and tools we end up using here, I do think it's really important that we agree (or discover we don't agree) on this point:
A crate that uses unsafe code, given that the soundness of its unsafe code has been proven beyond question, should not be treated any differently from a crate that has only safe code.
Simply showing badges for presence/absence of unsafe code, in the absence of any other information, obviously violates that. If we treat known-sound unsafe code differently from safe code, that makes known-sound unsafe code seem more dangerous than it really is, and makes safe code seem more safe than it really is. This is what I believe @nrc meant in his earlier post when he said "I think this would both demonise unsafe code beyond what is reasonable and give a false sense of security", which I completely agree with.
Obviously, we need to nail down what "proven beyond question" actually means, but that's the kind of detail I don't have any strong opinions on.