So they modified the keyboard to make it easy to detect what was typed? Not saying side-channel isn't a issue, but that's kinda silly :)
Like, if I can read Chinese as long as the strokes are clearly made, you can say that I can read Chinese. Now it's just a matter of increasing error correction to remove the qualifier.
It's only a matter of budget to be able to read the keyboard characters without modifying the driver.
Sounds to me like they modified the driver so that it had some kind of emissions pattern they could track. Driver could be modified via a virus or something.
It sounds like they just modified the driver to make those signals easier to detect. (i.e. A became 4Hz, B became 4.1Hz, etc.) If they had more sensitive detectors, maybe they wouldn't need to modify the driver.
My guess.