The status right now is that you have one identity for each service you interact with. If that service decides to ban you or goes down or you get your identity stolen, you lose that identity, but keep your identity on all of the other services you use. In the worse case, if you didn't tell people about your other identities ahead of time, they may still search for you and find you somewhere else.

If several services recognized your identity by virtue of having the same domain name, the fallout from losing that identity is much worse: you lose access to all these services at once, and whoever gets the domain name next will gain access to all of your followers and have a pre-built history. And if one service decides to ban you, you'll be exactly where you were if your identity was specific to that service.

So, with DNS-based cross-service identities, you are at best in the same place as having service-specific identities, and at worse, much worse off.

Additionally, a service which bans your account will typically not give the same name to a new user, or, even if they do, they will still separate the two identities / cleanup all previous posts. A DNS registrar will absolutely give the same domain to someone else if you stop paying for it, and any services which recognize that as your identity may not even know that a change in ownership has taken place.