>Profiles and posts are portable across hosted instances. If you have a problem with your admins, etc, you'll be able to hop away without much fuss.

As far as I can tell, this is only with cooperation of the server owner; since their "DID Placeholder" relies on a server to provide a string of identity updates. ActivityPub can do the same thing with HTTP redirects; and Mastodon supports cooperative profile redirection, which is morally equivalent. Polycentric[0] is a tad more decentralized than this, AFAIK it's specifically designed to make cryptographic keys first-class identities (so called "sovereign identity"). No clue if they've managed to solve the obvious pitfalls of cryptoidentity.

[0] Another censorship-resistant social networking tool being funded by FUTO Tech, of whom Louis Rossman is a spokesperson for