Actually, the the verifier (verifier.login.persona.org) runs code that could be run on any server. It _does_ check Gmail for the well-known file first, and then, since not found, uses the fallback of login.persona.org.
As soon as Gmail (or any id provider) implements a well-known file, the verifier will immediately use that instead.
And the script that does all this _could_ be run on your own server. The only reason we don't quite yet tell people to do that is to be absolutely sure the verifier is correct in every step. It's harder to get everyone to upgrade their own server, so while in beta, we offer the verifier.
As soon as Gmail (or any id provider) implements a well-known file, the verifier will immediately use that instead.
And the script that does all this _could_ be run on your own server. The only reason we don't quite yet tell people to do that is to be absolutely sure the verifier is correct in every step. It's harder to get everyone to upgrade their own server, so while in beta, we offer the verifier.