Someone should create a (dynamic) DNS provider (ideally a non-profit) whose only stated mission is to help people take ownership of their Fediverse, e-mail and XMPP identities.
If my identity were herrabre.mastodon.xyz (a subdomain instead of user-@), I could move to another instance by requesting a DNS record change, and my social graph would remain intact.
A trustable social contract would be needed so I kept effective ownership of the subdomain; the non-profit would be responsible for that.
The social network of the future: No ads, no corporate surveillance, ethical design, and decentralization! Own your data with Mastodon!