Because using a CA to issue a cert for you improperly is a good way to burn your CA. So it'll probably be used very carefully and in very limited scope because

Because using a CA to issue a cert for you improperly is a good way to burn your CA. So it'll probably be used very carefully and in very limited scope because it's detectable and leaves undisputable proof. For SMTP it's different since people aren't watching as closely. -- but then the CA angle is irrelevant because there's no verification. Though I'd be surprised if Google doesn't have some sort of program to look at these things and try to detect MITM or just gather info in general. Didn't they just add a little security indicator to Gmail? Google could probably single handedly force TLS verification on email by saying it'll increase deliverabiliy.