After a long process, the W3C Social Web Working Group charter has now been extended by 6 months so that ActivityPub can incorporate implementation experience, eg in Mastodon. https://github.com/w3c/activitypub
One place for talking details is the SocialCG, meeting in 1 hr. (Regrets from me for the first half of this week's meeting, sorry.) https://www.w3.org/wiki/SocialCG/2017-06-21