Have you considered a dedicated writing machine? The AlphaSmart Neo2 is well regarded as a distractionless writing machine. They don't seem too hard to find.

Otherwise, if you really want vim and emacs, you might consider trying to put something together that can be always on. S3 sleep is low latency, and can be lowish power. Or get an early x86 chromebook and boot to freedos; chromebook because the firmware is small and doesn't do much; x86 because software compatability; early because the earlier ones are easier to run 3rd party firmware on for better use of non chrome OS; freedos because it's small and fast to start (assuming it supports the chromebook keyboard anyway).