Facebook and other social networks are useful because they host your pictures. That is not as useful as it once was because phones have much more storage space and much faster networking than they did 7 years ago.
I'd like to see a social network app that runs on phones (and PCs, and even big servers for people who need major horsepower because they have a lot of "friends" like celebrities). Maybe with the ability to backstop your media on a variety of sources like dropbox, or even a bittorrent swarm of all your "friends" so that when your phone is turned off, or out of cell bandwidth (versus wifi bandwidth) your friends can still get access to your shared media.
Facebook is "over centralized" in that anyone on facebook is equally close to you all the same server farms - but that ignores the entire point of having friends. All we need is a system where your phone knows about the ip addresses of the people on your friends list. It is OK if it takes a lot longer find the people who are not your friends list because accessing their data is going to be pretty rare.