Product idea: I think it's just a matter of time that the basic e-reader technology will be so cheap that it should be possible to order one with a set of prepackaged books. You can read the books on the device, period. No internet, no word look-up (a dictionary can be a standalone book in the library), no highlighting / commenting, no adding or buying new books, no nothing else except the text of the books in the library. It will be so cheap that once you are done, you can just toss is out.
Why not a re-usable e-reader that reads books from an SD card? You can order or download books onto the cards, the reading experience can then be totally offline as you describe.