Is there any server actually using this so one can see it in action? They only seem to list Vervis, but the linked https://vervis.peers.community/ is down.

Last obvious activity on the spec/issue tracker is a month ago (fairly recent), blog six months ago, forum a year ago. Sounds alive, but not particularly active.

See my other comment at https://news.ycombinator.com/item?id=44896910 .. community involvement determines progress. Especially since the goal is to mature open standard specification for the ActivityPub protocol extension there is a chicken/egg. The spec has most chance to become successful if there are early adopters who embrace the vision of forge federation.