I have been advocating Discourse to add federation support in a bunch of topics on this forum, like here. With the Fediverse going mainstream now, and Tumblr and maybe Flickr and such adding federation support, the question is if Discourse has more interest for adding support as well.
I was contacted by the core developer of Flarum for advice on AP implementation and passed some links back, among which the one just mentioned.
PS. At SocialHub discourse forum, developer community for the Fediverse, we are looking for a long time how we can be part of Fediverse as separate forums have shown to be too much of a barrier for most people to participate.