Interesting thoughts. I almost went the Harmonyman route for that added feature (along with the sidechain input). But I decided that the PitchFactor was more versatile as a MIDI-capable multi-FX box. Of course, I have no idea about any future ET plans, or the R&D involved in that feature request. I get the impression that the internal resources of the PitchFactor are about maxed out.
I do something along those lines with MIDI CCs from an external pedalboard. It's not automatically triggered by pitch detection, but it's interactive enough for live playing and improvisation. Here's a post that describes the process over Depth/Key and Speed/Scale. You can map Pitch A & B intervals to footswitches in a similar way.
I don't know what you're using for MIDI input. In one type of configuration, my FCB-1010 can send two static CC messages per footswitch. I map pairs of the most useful harmony intervals to the 10 footswitches in a logical array, and call that up as a single bank (usually covering one or two presets, at most). Then it's a matter of latching the interval pairs as I play.
If you're interested, I'm sure that I have the Diatonic intervals documented by the exact CC value range. The Quadravox interval map is nearly identical to Diatonic – for Voices A, B, C, and D – with a small range carved out for the OFF position. At one point, I mapped out CC ranges for most of the algorithms and parameter positions. Each one has a different range; some with 128 distinct positions. 10 algos X 10 parameters X variable ranges of parameter control (and then some).
