gmane.org is gone. Therefore, all the links to John Gruber’s comments at CommonMark Spec (and possibly other places) are dead.
They all seem to be still available in the Wayback Machine (for example: Gmane -- Mail To News And Back Again), so perhaps all these links should be redirected there.
Nor is a PR needed…I had already modified spec.txt to use the archived links. This isn’t reflected in the most recent version, but it will be in the next update of the spec.