Hmmmm add in an Axo 
This eventually will have to spread, funny turn of events.
DIY MIDI Controller Kits - SoundForce Controllers
yeah, Ive seen these before, and thought they are a little expensive for what they are .
( though, in fairness, Im sure a good amount of development work was required, and its small volume)
looking at the DIY build is quite interesting, it looks like there would be space for an axoloti, (possible without midi din, since the height is probably the critical element)... and then you could simply, host the teensy with the axoloti and then feed connect the axoloti port to the external usb port. in the pictures they show the enclosures sides as wooden, so you may be able to drill through to then expose the axoloti ports. ( though I have to say the 'production' pictures, make it look like the sides are plastic, which I would find tricky to hack neatly, and for 199 euro Id want to do a nice job)
I think its a bit expensive, and a bit too tailored to the 101/juno 60... but could nice 
perhaps someone should talk to soundforce, perhaps an axoloti enclosure, with some sliders, knobs might be an interesting proposition for them. (they could ditch the teensy with axoloti)