For so many reasons, books should not be replaced. The most important is their permanence. So many copies, so widely dispersed makes it likely that our collective and individual literary history will survive in printed form, as it has done, in some cases for nearly 5000 years.
On the other hand, electronic communiction and files, while far more compact and useful in the sort term, have proved to be ephemeral. Change the hardware, change the software, the file is useless. Not to mention that storage media evidently degrades more rapidly than predicted.
On the other hand, The NYT article I read about the new reading machines suggests that travelers, business and otherwise, can pack a crate full of reading material on one slim reader, no net connection or special batteries required.
I should think that school text books could have a home on those machines - a way around 50# back-packs, obsolescence, and cost.
I doubt that I'll ever own one of those machines since I have Powell's books close by and hardly ever travel. But I suspect there is a legitmate use for this "tool" not to be considered a "book."
