If by worked you mean "worked so well they replaced all the big actors" then sure, nothing has worked.

But plenty has worked on a smaller scale. Raph Levien's Advogato worked fine.

There's also a reason most new social networks start up as invite only - it works great for cutting down on spam accounts. But once they pivot to prioritizing growth at all costs, it goes out the window.

PGP is niche. This would be far more mainstream. If you applied it to HN I could probably verify > 50 people already. For PGP I wouldn't know anybody...