I think everyone here has made it clear that optical is the best solution, so that's the direction I'll go for sure. The pedal is spring loaded, but the velocity is completely determined by the player throughout the cycle (a human isn't capable of lifting their foot faster than the spring will counter-react). The total cycle range up and down varies slightly by piano, but is approximately 1/2" ...and the pipe may also shift axis a bit during the cycle and not move perfectly up and down. Every piano is different, and I'll just have to figure out some mounting hardware which gives me options and play room.
So at this point I'm wondering if there's a generous person out there who'd be willing to do a quick sketch of the circuit this far, with the single LED and two phototransistor a, the timer pot for selecting the timeframe from 0-.5s within which the bottom phototrans must be triggered after the top one is triggered, the delay of the 10kHz burst from 0-.5s once it is triggered, the volume control from 0-1.4V RMS on the balanced output, the necessary circuitry for sine-ifying the burst and limiting it to 5ms in length, the ability to use the 48V Phantom Power from the audio mixer to power the circuit, and then some kind of summing circuitry to be able to combine the 10kHz burst with the signal from the piano pickup or mic without either one affecting/damaging the other.
If the summing part is too much trouble, leave it out and I'll just use two inputs on my mixer, one for the pickup/mic and one for the 10kHz burst...
Once again, the big idea here is that the piano player will depress the pedal, causing the LED on the pipe to move upwards about 1/2" and past both phototransistors, and then when the pedal is released, the LED will first move past the top phototransistor, and then the second a short time later. This time span can be arbitrarily determined, and only if the movement from the top to bottom phototransistor happens within it is the burst triggered. This burst will be used to trigger software on an audio mixer which temporarily mutes the piano pickup/mic because the dampers make a loud thump when they come crashing down on all 88 strings during most normal to fast pedal releases.
Thanks in advance, and thank you all so far for the great input and suggestions!