Are you serious? A social network is already decentralized by its very nature. Facebook is not a social network.  Facebook is just a social network mediation service.  The only reason people use a centralized website for that in the 00s and 10s is because websites are easier to program and maintain and the technology of p2p applications hasn't caught up yet, especially in terms of UE.  Trolls and spammers are not an issue in a high trust environment where you get to choose who is allowed to communicate with you.  They have only become an issue for Facebook users who don't use Facebook as a social network, ie. people who have lots of strangers as Facebook friends.

I would be very surprised if 20 years from now social networks are still mediated by centralized websites. Everyone is going to have their own agent that communicates with other other people's agents via standardized interfaces. The power and flexibility offered by agents is no match to a one-size-fits-all website.

As for decentralization of leadership, I agree that there is no replacement for a human leader when it comes to giving a group of people vision and inspiration.  One aspect of leadership can be decentralized though: power.   Democracy is an attempt to do just  that, though it didn't quite get there because it still relies on human power custodians.  DACs could take this one step further and replace the custodians with consensus networks.