Amazon could suggest it but at the moment the Agency Publishers have contracts with Apple, Kobo, and other retailers which forbids any eBook discounting.
So unless those contracts expire or are re-written - it isn't viable at the moment.
And again, it was the Publishers who insisted on the Agency Pricing/No Discounting model so I don't think it'd go far.
It is an idea that comes up occasionally. I've never been under the impression that there are huge numbers of people who'd be interested. I could see it for the textbook market and a few other limited markets but not for general book reading, most people simply don't want 2 copies of a book.