> Question: If we did do such a thing, what controls would everyone want....
I'd recommend looking at the interface Mutable Instruments Shruthi implements.
http://2.bp.blogspot.com/-1zHRPTZH7B0/TzZUV_LBg3I/AAAAAAAAANE/lPglGaVH6-U/s1600/DSCN1183.JPGMaybe reduce it down to one encoder with push down switch, 3 pots and 4 switches.
You'd make the OEM switches navigate the LCD menu to, right?
I'd think you could create a tidy editor/realtime controls with re-assignable pots/encoder via soft labels so you had pages of groups like-
Cutoff Resonance VCF Env. Depth (show as CtOff Res EnvDp)
LFO1 Rate LFO1 Depth LFO1 Delay (show as L1Rt L1DP L1DL)