Downsides are field performance...
As much as I like the innovative (VFW 614 apart) concept of the aircraft, the takeoff distance of almost 4000ft quoted in that Aviation Week article for a light jet is a clear showstopper around here. What does anybody need a "lavatory sink with running water" for if he can't fly the aircraft in and out from the closest airfield? And 5+M$? Really?