I think even more useful/smart would be a single M.... an M1... just one efx module
you have an M13 and need one more module you get the M1
you have an M9 and miss the efx loop of the M13 you get the M1
it could very small.... I think they would sell bazillions of those.
They kind of sort of had that with the ToneCore pedals where you could switch out the modules, and they had the DSP developer kit thing. The only problem with that is that it wasn't all that flexible. If they did have a single effect that could be changed to any effect in the M series, that would be sort of interesting. That would make it kind of like the Yamaha Magic Stomp that's been around for several years. I guess the one thing to consider is the price point. At what point would people just decide to get a second M9 instead of picking up a smaller pedal?
I really like the idea of an M1. Amidst your pedalboard would be this little wildcard that could add the perfect touch to a sound when you need it.
Stereo effects removed so that there would be only three plugs on the back: In, Out, and a single expression pedal input. Optional 9V battery. USB for updating instead of MIDI. No Scenes.
10 second looper, dedicated to a new model type(white background). Press to record. Press again to overdub. Hold to delete.
Something like this Maybe a bit fatter: