it is an interesting idea, - also, to be cynical, another great way to collate email vs physical address, but the likes of ebay, also do that, so my opinion is not intended to be 'that' critical, just thinking out loud...
I also have to say that I'm not sure if I want to lose my 'real' books, some of them get read again, and again - many are available 'virtually', anyway & sometimes I prefer to read them on screen, as well - it's complicated