If I understand correctly, this proposal uses a globally-shared append-only log (like the Bitcoin blockchain) as a shared cache of server keys (like SSH's caching of the key first seen with a new endpoint).

Once the 'right' key is pushed into the global cache, you can't fool any users who can access that cache.

Revocation or recovery from the 'right' key itself being compromised or lost is still not really handled, though some ideas are discussed in the draft design. But at least later Certificate Authority compromises can't ruin the security provided by a server's declared long-lived key, once it's been registered in the global cache, as long as the server itself manages its own key well.