Within the next 10 years, and maybe much sooner, the vast majority of content on FB/Twitter/Reddit/LinkedIn will be completely fake. The "people" on those networks will be fake as well. Sure there are bots today, but they're not nearly as good as what I'm talking about, and they don't exist at the same scale. Once that happens, the value of those networks will rapidly deteriorate as people will seek out more authentic experiences with real people.
IMO, there's a multibillion dollar company waiting to be founded to provide authenticity verification services for humans online.
The US government does authentication in real life via social security numbers. Of course, they are not very secure: a government-operated SSO or auth API for third-party applications would be a logical next step.
It would guarantee uniqueness and authenticity of users. Even better, if this were an inter-governmental program, it would deter government meddling: a state issuing too many tokens for fake accounts would arouse suspicion.