But this is already not happening. Textbook publishers are already giving students a choice to either buy a textbook outright or "rent" it for dramatically lowe

But this is already not happening. Textbook publishers are already giving students a choice to either buy a textbook outright or "rent" it for dramatically lower. This is already happening with physical books. I'm sure the publishers (at least some of them) would love to come up with some similar scheme with digital books.