Usenet still exists, but herding cats never got any easier, and the cost for hosting didn't go away. There is a reason it became marginalized: user experience.

Facebook Zero is no longer doing what you allege, and never actually did. It was just a plan that was scrapped.

Diaspora never had a design or plan to work. It was a couple college kids who thought it would be neat despite never having written a distributed protocol before. We've had lots of smart people attempt this, and haven't gotten anywhere close to a usable "distributed" social network prototypes.

If your idea can't bootstrap itself from zero users the way modern startups work, maybe it isn't such a great idea after all.