Basically, I'm proposing a peripheral that enumerates as an USB keyboard but uses voice recognition instead of keypresses for input. Put a good microphone, a hefty Blackfin, and some EEPROM (or have an SD card slot, so dictionaries can be swapped in and out) on a board, perhaps with some (chordable) buttons for additional input. Load the open-source speech recognition engine PocketSphinx on the Blackfin. The processor is dedicated to speech recognition, taking the computational load off the laptop it's plugged into. Note that this is a technologically naive view: I'm not actually sure this is easily technologically feasible (I can find out, but don't have time to right now.)
In order to use it, you'd speak into the microphone (or press a button while speaking into the microphone) when you'd normally type; the Blackfin would translate this to text and either push it out over USB directly or stream the data to a PIC that logically chunks words and translates them into commands ("enter" would get turned into a newline, etc.) and sends them out over USB.
Okay. I think I can stop thinking about this now. Back to work.