I'm not sure what useful purpose it would serve, but I had an idea come to mind, so I am writing it down for posterity. An Envelope EQ. We have envelope filters controlling flangers, phasers and tremolos, but what about the humble EQ? What purpose could this serve? Maybe you could have the bass sound very different when you get to playing heavily. For quiet/normal parts, maybe you have the normal sound of the bass what you want, but beyond a certainly sensitivity, you wish the mids were dropped a little, or maybe the bass was enhanced...but only during that period of heavy playing. And without having to dance on the pedal board to activate/deactivate.