Technically you are right, but in practice a multi-line List-Id seems likely trouble, and the comment isn't really that useful as people sort on the token. Changing description to "chirp development" wouldn't lose anything and would avoid trouble, even if the people having trouble are wrong.
You realize I am running industry-standard mailman for this. I'm not generating the List-Id header, so I have no control over it. Feel free to file a bug with them, but I'm nearly positive they will close it since it's not a bug :)
And, if you are going to be strict about RFCs, the From: field must contain the sender, and not be forged to be the list. See myp private reply about not modifying subject and body -- with that change, DKIM works and there is no need for kludges to avoid DMARC trouble.
Yeah, unfortunately that's just not possible in the real world. I get a ridiculous number of emails from people who can't figure out how to unsubscribe despite it being in the footer, close to where they clicked on the site-owner email address to complain to me. That's down to like 10% of what it was before we started putting those in the footer (on the users list).
So yeah, it'd be nice if Google and friends hadn't broken the internet with DMARC, but they did. And, these are all the same behaviors of the list before this.
--Dan