This is an idea I’ve had (and researched pretty thoroughly) since freshman year in the dorm: the ultimate tool for writing text. A “real” computer is overkill, and an iOS device, with its color LCD screen and multitude of apps, isn’t ideally suited to be a tool for writing text. What is needed is something closer to the Kindle: a (mostly) single-purpose, self-contained device with an always-on wireless connection (whether that’s through 3G like Whispernet or through WiFi) in which every facet of the design of the hardware and software is geared toward one thing: being an efficient tool for translating ideas into words. Essentially this device would be the translation of an application like Byword or TextMate into hardware.
I know iOS (and OS X Lion) can offer a full-screen writing environment, but just past that layer is a world of possible distractions.