This is a directory of public keys, which every secure messaging app including Keybase must also have, but federated rather than centralized. That's a necessity for e2ee and it's very cool to implement it as an append-only version of the pub-sub messaging the fediverse already has.

It has nothing to do with the identity verification a la Keybase, unfortunately, as that would be a really good and useful feature for the fediverse, but I think it would be a lot harder to do.