I believe Glockenlang has a different slant. In active mode, it boosts and cuts, but acts like a tone knob in passive mode. It would be kinda nice if treb knobs were push pull to allow for the active or passive cut. Sure, you could always add another tone knob, but if possible, I like to get things done with 5.
I don't see why you couldn't use a 'stereo' (two channel) single pot, and have half in the active circuit and half in the passive circuit, controlling whatever you wanted.