@the-erc, thanks for the technical ideas above. Yes, some switching + logic may work. I've also been considering if some combination of latching or latching switches plus logic would work. All told, I probably have to just mock up some draft patches IRL (when possible module-wise) or on VCVrack and test what I can get to actually work. Part of it is getting clear on the logic / signal aspects of it, which I could maybe work out with pen & paper (& beer & cats).
@Lugia, yes, the little Fux book is alongside a few prized others in the counterpoint section of my music library. I hadn't really thought about pedal point seriously for a while as it is not an obvious fit with my focus genres. But yes, not to be ignored. And I love it in the Bach and Hindemith organ works.... BTW, any other technical ideas / responses to my longer ("step 1-5") post above? I know you a day or two ago said you were mulling it over. Your ideas & draft rigs are always interesting food for thought.
Thanks folks!!!