[zzzcpan]

You are talking about lower layer protocols here that don't matter for decentralization. In fact, a decentralized transport protocol can be made that doesn't require your ISP to give you an internet routable IP address nor put you behind NAT.

Think e-mail, for example. It never required you to have an internet routable IP addresses to communicate with anyone. There were and are plenty of local networks where people run local SMTP servers that communicate with upstream SMTP servers over local network and only those have public IP addresses to communicate with SMTP servers over public internet.