>> 1) I hear that that PC keyboards are "scanned" and therefore
>> quantize inter-key timing measurements.
> Every matrix keyboard has to scan, and thus does have some sort of
> quantization.

I'm not sure this is actually true; I think I could probably design a
non-scanned matrix keyboard.  (It would be a bit contrived, but I think
it would be doable.)

> Every serially-connected keyboard (or terminal) does this.

To the extent that this is true, it's is a common accident of
implementation, not anything necessary.  There's no reason why keyboard
has to be scanned, or even matrix-encoded, just because it's connected
to its host through a serial interface.

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