This would really only be useful for a one off transaction, not an ongoing delivery process.
Agreed. It's designed primarily for e-execution of contract documents which can be handled under UETAs & these state laws lack ESIGN's demonstrable consent requirement.
The OP was interested in e-delivery of appraisals, however. Since federal disclosures (such as appraisals) can't be e-delivered under UETA standards, that brings us back to ESIGN and the same drill that would be followed in order to consent to e-delivery of periodic disclosures.
Delivery of preconsent disclosures and a test drive are always possible--even in an email-based "one-off" system. Before sending the email with the "live" attachment, the bank would send an introductory email. This message would contain all the preconsent disclosures and have an attachment of the same file format as the "live" document. Following the list of disclosures, the recipient would be directed to open the test document and retrieve a PIN or other unique bit of information. By returning this unique code to the bank (by any electronic method), the recipient "reasonably demonstrates that (s/he) can access information in the electronic form that will be used to provide (the "live" document.)"