I know that. It's just depending on domain name "ownership" (and even though it's called so, it's temporary lease, not purchase of property), in exactly the same way general audience depends on email account "ownership".

Except for the fact, if one's email account or the whole provider goes down, they should still be able to login with old-fashioned password credentials. With Persona, unless the site has a backup authentication method, they're out of luck.

This effectively means I've to stick with my domain name forever.