I understand the sentiment but simply because a solution doesn't cover all use cases (users must be able to change email addresses) doesn't mean it can't be usa

I understand the sentiment but simply because a solution doesn't cover all use cases (users must be able to change email addresses) doesn't mean it can't be usable. Also, we constantly use services were you cannot change your email address because that's how the system identifies you, so this dependency of email addresses isn't new at all. (One work-around would be to use an disposable e-mail address service and redirect your emails as needed.)