Hey,
You are offline? What does this mean? in a local network, not
connected to the internet?
No, I'm not offline. I'm fully online and connected to my server as
usual. I just think to synchronize offline history, which could be a
lot of data and include confidential messages that were initially
encrypted, an encrypted direct client-to-client channel would be
cool, both for speed and security.
If I understand you correctly, you are suggesting that both clients should be online while synchronising their history. If we are talking about a protocol that is supposed to work on all kinds of devices, this is a flawed approach: keeping iOS (and, increasingly, Android) applications online would be very inconvenient, and you wouldn't be able to create a decent user experience with such protocol.