Seems like if you shrink the bezels you can fit that HD 6.8" screen into the current dimensions of the Paperwhite. I'd also like to see them get rid of the 'inset' of the screen, so the screen is flush with the bezel and the device can be thinner, and crud would not get stuck in the corners. Of course tweak the touch response so it ignores your thumb resting on the edge of the screen, which now extends nearly edge-to-edge.
If they could get rid of the bezel altogether (at least on the sides), so much the better.
Then make a bigger version of same (9-10").