That's an interesting idea, when I built my Fuzz Face, I put a pot in it to simulate a partially drained battery. The tone is noticeably different depending on how that is set.Have I haven't updated in a bit so you may already have done this to the drive blocks but have you thought about offering a "voltage" setting on drive blocks...from starved to all the way to say...24v?
I also have a "Danelectrode" which is a power supply that allows you to reduce the voltage. It works really well with my RAT.
So I can see having that kind of feature in the drive models, it might add some interesting tonal variations.