A public protocol and a reference implementation of a social network. The problem is stabilized, it's time to do to social networks what SMTP did to email. Open it up to be fully decentralized, where people can host their social hub or use a hosting service, of which there would spring up a multitude.

Social networking is nowadays as central to the internet as email, and it is the first such, heavily used, application layer "protocol" that is closed.

For a small period of time I had hopes that this would be the path G+ would take to the top. It isn't.