I don't think we should try to bridge the current mailing list with a Discourse instance. One heavy blocker is that the Discourse instance will not accept incoming emails from people who are not registered on the instance.
If someone wants to set up a Discourse instance dedicated to the Org community, please go for it -- we don't "own" the community. We can advertize it like we do for SO and reddit here: https://orgmode.org/worg/org-web-social.html -- Bastien
