The MicroArranger was IMO a missed opportunity. Placing the failure-prone bender to the left of the keys instead of above them makes it nearly as wide as a small 61-key keyboard with "full-size" keys such as Korg's own Kross.

The most portable arranger I can conceive of is a 32-key controller for the right hand (F1 to C3, probably 7/8 size keys) and a similar two-octave keyboard for the left hand, arranged "organ style." A foot switch or MIDI foot controller could take care of voice and program changes. You could almost play this while sitting in a coach-sized airline seat!

The keyboard controllers would drive a BK-7m or SD40 module, perhaps vArranger on a laptop, etc. The whole thing would have to run from some kind of battery pack, with voltages tailored to the various hardwares. Build it and I'll buy one!