It's also in the nature of early adopters to move on by the time a product or service becomes too mainstream. They just need to see something else that is compelling first. But I think many of them are already using it much less than they used to.
I think a true distributed P2P social network would be very interesting for them, but it would also need to get the execution right. I haven't heard much about Diaspora lately, but something interesting came out a few days ago with BitTorrent trying to make a P2P social network around torrents. I think that's an intriguing idea, and it's a bit similar to what Opera tried to do with Unite.
As a side note, I think all social networks so far have had one major design flaw. I've joined other social networks before Facebook and they all seem to suffer from the "too many friends" problem, which does become a problem once you start having hundreds or thousands of friends.
I think there needs to be 2 categories of "friends": true Friends and Followers. When you accept a request it should make that person a Follower by default, but it should give you the option to make him a Friend also. So many people add others on Facebook now, when it's just so they can see more info about them or their private pictures, with no real intention of "befriending" them later on. That's why I think most requests should become followers by default, and only choose to make them "Friends" when you really know the person.
I think Twitter's model works a bit like that. You can have thousands of followers, but only a few "friends" where you basically follow each other. Just something to think about for whoever wants to build the next social network or whatever, so they don't repeat this huge mistake that almost every social network has made so far.