Thank you @aschrijver for these interesting reads.
I did not want to create yet another account at socialhub to reply to https://meta.discourse.org/t/community-has-no-boundary-discourse-as-a-fabric-ideation-brainstorm/174578 please allow me to comment here.
Regarding linked open data and forum communities, I would like to mention http://rdfs.org/sioc/spec/ Do you know activitypub applications that use it?
Regarding single sign on and identity management, do you know WebID ?
Regarding the manipulation of the same data using different applications, I suppose you know https://solidproject.org/ How would you compare it to your ideas about federation ?
Regarding tags / topics to categorize threads, have you thought about using dbpedia or wikidata urls in place of tags or using the SKOS vocabulary to exchange hierarchies of tags/topics ?
In your post, the part that interested me the most was the section “Fediverse integration”. Could you point me to more ideas/thoughts along the same line ?
Last but not least, we are considering adding ActivityPub to the https://www.cubicweb.org framework in 2021 and any suggestion will be welcome 