I've always wanted an ultra-low-power dumb terminal using eInk paper displays - something you could hit days of runtime with using a small battery pack. eInk uses no power when they're not updating - so idling or long-running operations would hardly use any power.
So far the easiest approach I've found is using a hacked Kindle with an attached keyboard. You can run a terminal client on it and ssh into another system, which I think is a sensible access mode.
Ideally, something like the AVR PicoPower microcontrollers would be fantastic - they run on ultra-low-voltage, eat 1 mA/MIPS, and idle down to basically nothing (<1ma active and a few dozen microamps during sleep). ssh is probably out of the question but I could toss a VT100 stack on it. Unfortunately the eInk display is the hard part there - most eInk parts have very poor documentation.