As I wrote in another comment, portable identities are a matrix spec change I'm quite excited about: https://github.com/matrix-org/matrix-doc/blob/neilalexander/...

Start on a server, but your real identity is attached to a cryptographic key, not an e-mail-like identifier. That would allow you to move around, and maybe one day get rid of domain names altogether (using something like yggdrasil or tor to host and connect servers, for instance).