However I think it might still confuse customers. A normal user expect to be able to change their email address on the site where they do business and the "MAGIC". I think we would have been better of requiring a username, email and password, rather than using the email as the username. For a large number of people needing to have both username and email seems redundant and stupid, for real life customer... not so much.
My issue is, a customer has X number of orders on our site. Then he/she changes email and expect that using the new email address the old orders are magically available. This seems naive but that is what you have to deal with.
Again I should check to see if Persona indeed maps multiple emails to the same identity. It didn't seem like it when I tested it last, but I would not rule out that I did something wrong.