You know, one crazy idea that would suddenly make this work a WHOLE lot better for me, though I know it would add to weight and complexity: make the iPad in a tablet style, where I could flip open and twist the screen lid around - and have an e-Ink display on the opposite side for eBook/PDF/Doc reading. As light and ultra-thin as both the LED backlight and the e-Ink display are, it's do-able, though the mechanical design and weight would become more critical.
No need to have to flip it over!
I don't think they're in any shipping products yet, but Pixel Qi has been ramping up their production lines so hopefully soon. Essentially it's an LCD/e-Ink hybrid... when the backlight is on, you get a full color LCD. When it's off, you get black and white, low-power e-Ink.