A multi-page e-ink book would be nice. I love my Kindle for certain types of reading, but when I read, I like to flip back to previous sections. Search doesn't work because I rarely know verbatim what I'm looking for or the search terms are flooded with answers from the entire book, when I really want it narrowed down to a particular area. With physical books, I just remember roughly how far into the book it was and can jump back there and start searching. I'd love to successfully replicate that with a Kindle.