Also important that an initial smaller community would be targeted and that it would succeed there. FB did this will colleges, a federated one would in a world where FB already exists would have an even harder time.
Depends on your definition of "distributed", I suppose
Keybase offers decentralized trust, in that the Keybase server can't lie to you about someone's keys -- your Keybase client will trust their public proofs and not the Keybase server -- but it's not a distributed/decentralized service as a whole, because you still receive hints from the server about where proofs live, and learn Keybase usernames from it.
(I work at Keybase.)
No, I don't think the tech is quite there yet. Even just handing out human-readable usernames requires blockchain-style consensus, and we don't have a blockchain being followed along by everyone's machines to adjudicate consensus requests (yet!).
The folks at Blockstack Labs are doing fine work in this area, though: https://blockstack.org/
The fact that it failed at the most basic thing of actually telling what it is about, what it does and how would be good reasons to not use keybase.