I think the "feed" aspect needs to be considered also. The power of Facebook, Twitter and such is largely their feed. The feed is an answer to point #1: grandp

I think the "feed" aspect needs to be considered also. The power of Facebook, Twitter and such is largely their feed. The feed is an answer to point #1: grandpa simplicity. The feed is the thing that needs to be protected from points #2 & 3: identity and culture. The feed is that will motivate participants, content creators, etc. IE, many will create content for the feed. Reddit/Digg/HN upvoting were a simple way of doing the feed that proved this point and paved the way for Facebook & Twitter. A lot of mass adoption services created after went extreme. Feed only. The Tinder UX is a feed of datable people, for example. Spotify's importance is being solidified by being a feed. Importance in spotify's context is largely "being the place where music gets popular." One way or another, the feed issue must be addressed. New content UIs will either have a successful feed or transcend the feed some way. I'm not sure how this relates to federation. A feed seems a centralizing element by nature. Successful federated systems of the past (the the WWW) tended to leave the feed ("discovery," in a pre-feed context) to someone else... which turned out to be google, fb, etc. However the labyrinth is is designed, what matters is how the feed works.