WeChat doesn’t provide the linked email address to the developer as I know.
Of cause, we can always prompt the user to enter an email address after scanning the QR code to login then require the user to verify it that’s what I said link to an existing account. But do we really benefit from it? Or just annoy the users?
There are few really old solutions at Github
And I don’t think the team is very interested in it, you may better post a job at Marketplace.