That is certainly a very useful service.
I think the solution need some improvement, because:
1. The system relies in a third party person. What happens if the user loses the qrcode? Or even if he becomes unavailable?
2. What if the system send the e-mail, but the user doesn't see it (mail server error, spam inbox, etc)?
3. What if the server/domain goes down? This type of service must the the most reliable possible. Maybe a government funded project could address this.
I hope you find solutions for these problems.
Since you touched this subject, Google has a service that aims the same, but the validation is different. If the user doesn't access his account after n months, a phone call is made to the user AND an e-mail is sent to someone the user choose.