[nikkwong]

But let’s say for example your phone and your computer are clients, and your computer has latest version of your data. When you open your phone, if your computer is not on the internet, you won’t be able to get latest. So, would this be practically useful for a terribly trivial use case like this?

[gpm]

Have a server be just another peer, not privileged in any way, but always online and available.

Maybe do the routing through a distributed hash table like we use for finding torrent peers (perhaps even the exact "mainline" DHT torrents use), which would mean that even with the server being down you could still sync with your other online clients.