In which case [the message body link] would be set to something like.
Just for fun, I did a trial implementation. It works, but the URLs are too long. For example, the URL below spends 59 characters on the messag-id, and 27 characters on the listname. We're already over my comfort level (of about 72 characters) and haven't even started to count the hostname, and other URL-lengthening overhead. Maybe this was a bad idea after all.