What seems to be an overlooked part of Mailman 3 is its REST api. I am actually developing a brand new admin U.I. called Affinity to replace Postorius. Empathy will be the forum/archive replacement for Hyperkitty. I want Empathy to be patterned heavily after Discourse. Affinity/Empathy will have great virtual domain support and a very strong mailing list core (Mailman 3) that Discourse seems to be lacking. BTW, I migrate MM2 lists to our MM3 service all the time.
This Mastodon instance is for people interested in technology. Discussions aren't limited to technology, because tech folks shouldn't be limited to technology either!