The 80/20 solution would be to "just" free the authentication aspect from Facebook's control. If Facebook were forced to support something like OpenID Connect,

The 80/20 solution would be to "just" free the authentication aspect from Facebook's control. If Facebook were forced to support something like OpenID Connect, then anyone with one of those IDs, from any provider, should at least be allowed to log in to Facebook and view posts from their friends who have accounts there. Facebook would be forbidden from storing any information about you, except for the fact that your friends on Facebook had manually specified your ID as someone who could view their posts. If your ID provider also ran a social network, and allowed people to log in with their Facebook accounts to view your posts, then that would cover a lot of use cases. The next step would be to allow/require Facebook to fetch RSS-style feeds of events from your social network, so that Facebook users would be alerted to your new posts, without having to manually browse to all the different sites that their friends are on. This would require more engineering work, but could perhaps be implemented as a browser plugin. At some point, if Facebook are making it unreasonably hard for competitors' users to interoperate with users on Facebook, there would be grounds for an anti-trust case against Facebook, which I'm sure the EU would be happy to consider.