Yes, Apple stores already do this as you mention. The details are really difficult, though. For example, someone returning an item but they gave an invalid email address the first time through. Etc.
I agree, and that's part of the problem I think I'm trying to solve :)
Some of the things I'm throwing around with my buddy is possibly having an mobile app as an endpoint so that email addresses don't have to be given up at the register. However, I believe in trying keep simplicity as a priority.
There is absolutely a demand for it, though. Especially with small business owners. I know a couple that have asked if something like it existed because come tax time, sorting the large number of receipts to either do yourself or hand off to someone else is difficult. Or if they choose not to do it, their tax people have charged extra for having to sort it all out. an email system would probably allow for better sorting too, I'd imagine.
Some of the things I'm throwing around with my buddy is possibly having an mobile app as an endpoint so that email addresses don't have to be given up at the register. However, I believe in trying keep simplicity as a priority.