But make it the first one with a treadle that ramps up the gain and ramps down the boost so the levels stay the same or close to the same. There would need to be an adjustment pot for overall boost. Ideally, gain would become more saturated with a slight increase in signal strength because I like solos and such to stand out a little in the mix live.
Another idea is an OD that splits the signal and applied several different OD's at the various frequencies then remixes them to the final signal.
This is all dependent on whether you can actually build an OD circuit that has a good basic sound but I've owned your pedals and you guys get a good saturation that I found really usable so I have faith!
You could go for something like the idea I had last night: a "sort of" tremolo that doesn't affect the output volume like most tremolos do, but rather applies gain in a rapid up-and-down pattern. While the signal level remains more or less constant, you'd be going in and out of distortion as rapidly as you want - which would be a really cool sound for long, sustaining notes.
There's also always room for a two-mode fuzz + octave fuzz pedal.