My thoughts : Social networks as we understand it today will no longer exist. There would be cyclical phases of fragmentation into specialised services and localised networks with attempts to bridge them via a common ^standard^ but of course that won't work, because history.
The role of the web itself as the platform where social networks live would diminish further than it already has. Of course everything would still be connected and online on the Internet, but the web won't be the primary home for these networks. I am doubtful about AR and VR playing a big role. These technologies still are waiting for thier iPhone moment to occur. When it does, I doubt it would be related to social networks.