@alshafei@simplex this is great, thanks for posting it! Always glad to see improvements in privacy protocols, especially when that includes metadata.
This can almost be used as the transport for a social media system to replace FB private posting. The piece missing is efficient one-to-many message delivery; right now their group messaging is limited to small groups since (as I read it) the full message is encrypted and sent to each recipient separately. Ideal would only require one upload per message, which the receiving server would then fan out to the recipients. You can do this while keeping e2ee by encrypting the full message once, then encrypting that decryption key for each recipient, for a total overhead of 32 bytes of encrypted key material per recipient. (Maybe this already happens and I missed it.)
A smaller concern is that if there's only one server on the delivery path (i.e. 2 hops) then that server sees the IP addresses of both the sender and the recipient. Using Tor mitigates this.