What I'm seeing start to happen is something about the size of a checkbook, less than half inch thick. One entire side is an eight inch screen, perhaps with touchscreen. There are some controls on the sides, and more on the other side, including also a telephone touchpad, camera lens, etc.
I think that's where the evolution is going. Pocket sized, useful for EVERYTHING. And reading html, pdf, etc without need for reader programs. And a slot, usb hookup for getting books for those who don't have to wifi everything.