Form validation if email address exists

It seems like OP Membership Sites with Open Enrollment enabled have the ability to identify if an email address exists or not on the login form. It would be awesome if on Smartforms/Orderforms we were able to have a setting for the email field to validate if the email address already exists in your OP account. That way in cases where the customer already has purchased in the past, you can notify them when the email field is filled out that they already have an account.