Gmane is a mail-to-nntp bridge, so Discourse actually doesn't have to support nntp to allow reading/posting via Gmane. It just needs a rather careful setup of the gmane subscription address to the mail-interface of Discourse, and it's not completely clear to me (yet) if it can be split out into a good dozen lists, like we now do. Should be possible if people tag their posts correctly, but needs some experimenting probably.