A relay is a service.

I need to be able to switch service provider, at any time.

When you make the relay url the ID, you need to own a domain name to switch services under the hood. And even then, you're still not really sovereign.

When you make the key the ID, you only need that to switch relay, blossom server, mint, etc... Same pattern for everything. Same pattern to teach my customers, once.

I'm not talking about switching IDs.

That's the same problem/opportunity we have for profiles in general.