Kindle and nook both have a lending system. While your book is lent out, it cannot be read by you. After 14 days, the book is automatically disabled on the other reader and reenabled on yours. Is this correct?
So technically, I don't see why the book can't be permanently transferred to another person, at least one using the same ereader/DRM scheme. As for payment, that is up to the private parties involved.
Of course NOBODY except the consumers want this, which means it's not gonna happen
