I like the multi dimension controllers. To work with current specs, I understand the choice to work with note-per-channel.
But as far I understand with the versions of controllers out there now, isn't it so "we" only need 3 extra controls which are poly (as in PolyPressure).
Poly X = movement on the X-axis of a "key" (Like on the Yamaha GX1 solo keyboard)
Poly Y = movement on the Y-axis of a "key"
Poly pitch (or Z). For those controllers which have ribbons. Those ribbons could control something else than pitch right?
By having these messages, you don't need to take away the other channels which could be used for another synth. At the moment there are no hardware synths supporting this, but imagine in the future you can have a multi timbral synths with all the controls on any channel without the need to program the synth so that on multiple channels the same patch needs to be selected to be able to use MPE. And losing the multi timbral function because of the note per channel choice.
I my self use TouchKeys (https://www.kickstarter.com/projects/instrumentslab/touchkeys-multi-touch-musical-keyboard
) which work quite nice. I can imagine something like this can be implemented in a real keyboard (like Fatar keyboards). By using this touch sensitive material embedded, the PolyPressure becomes cheaper to implement AND having an X-axis and Y-axis for extra control.
If something is not clear, I am happy to explain more.
Best regards, Marcel Krol