I like Steve's idea. I've had the thought before, that I'd like all of the hardware put into a pocket sized device and have the screen and it's controller chips and battery separated from it, but streamed data via a short range, high-speed wi-fi link. The overall weight would be higher, but the weight in your hands would be less.
An EInk display would be different to an LCD. But, one solution would be to run the display from within a dedicated application which only exposed select elements of the OS to the screen. That technology exists today.
This EInk display runs exclusively from within a Vista sideshow Gadget.