Question: what about crossposted messages?
Let's say a message gets sent to a list called mailman-developers with a CC to a list called pet-bunnies. Hypothetically, of course. Presumably, the person who got the message from pet-bunnies should probably end up at the pet-bunnies archive, where the message can be viewed in proper context; right before the processed carrots flamewar and after the manifesto on proper hopping technique. To make that work, I think we need some way to - at least optionally - allow one or more of the RFC 2369 headers to influence the archival URL. Reading the wiki, I guess that's where List-Archive comes into play?
My other question is about the angle brackets. Barry, why are you inclined to include them in calculations? It's kind of arbitrary, but quoting RFC 2822, end of section 3.6.4:
Semantically, the angle bracket characters are not part of the msg-id; the msg-id is what is contained between the two angle bracket characters.