Just to be clear, this is never going to happen. We do not live in a world where computers are for "computer people" anymore. I've been running my own mail server since 1995, and I would not wish it on anyone.
Running my own mail server has not helped me with:
1) Metadata protection. Every email that I send or receive either has Google or Yahoo on the other end of it. Running my own mail server does not help me "own" my data at all.
2) Data protection. Federated protocols can almost never change (look at the history of IRC, XMPP, SMTP, HTTP). Email is stuck in time, which is why emails are still not encrypted. WhatsApp, on the other hand, had the freedom to deploy e2e encryption to over a billion people very quickly.
3) Censorship circumvention. Email is very easy to identify and filter using DPI. In a world where people are only doing host-based filtering, blocking 100 or 1000 hosts is no more difficult than blocking one. Whether or not there is "a finished list," if people can discover these services, so can the censors. It is much easier for the censors to add a single line to a block list than it is for people to switch to an entirely different provider with an entirely different namespace and try to rediscover all their friends.
If your idea is that every time a host gets blocked, everyone could move to a new one and somehow rediscover their entire social network, it would be way easier just to use a centralized service and access it with different VPNs as they are successively blocked instead. That would prevent you from having to rebuild your entire social network each time, but is still a terrible UX.