A pinch point is battery life. Rapid character input is another pinch point. Accurate pointing too. Client system emulation. All pinch-points in using a portable device as a development machine (Y Combinator YCRFS 5: Development on Handhelds). One thought is to break the problem into two contexts; the portable context (walking, driving) during which you will rarely be developing and arriving at a destination suitable for developing (office, home, cafe, bus, train, plane.) Identify the pain points of each (fitting in your pocket for the portable context, input and screen-real estate for the second context) and seeing if a device can be made to adapt to both at different times. Sort of like those pull-out PDAs the actors had in Earth Final Conflict. Battery life is a problem only if a: the power cord is a pain to carry around and b: the battery can’t survive between recharges at locations where you can get power.