Just, so you know :
3 -> doesn't need to be permanent, it can be changed
5 -> Signal has developped the most secure e2ee im protocol.
5 bis : about Matrix, XMPP the servers can't decypher messages when e2ee is enabled
5 ter : "p2p" by itself doesn't define any kind of encryption, I don't understand how you can compare carottes with potatoes, and thinking that's a fair one. But if you insist, take a look at syncthing and its possibility to not trust a node.
"Dependence on DNS" : about p2p, please learn how they work before writting this. I mean, I don't know, take a look at torrents, you don't need the hostname for reaching a node. Trackers aren't mandatory, there are other ways to discover nodes.
Also, just so you know, DNS is one of the most central part of internet with BGP and NTP, being dependant of them isn't a bad point.
