Good question. Actually - it might not even reduce productivity. Suppose you put a terminal where you run commands on the average every ten minutes on one such screen positioned on a fully 3D positionable robotic arm. You lose maybe 2 seconds finding out if this time is it is over your left shoulder or up right on the ceiling. But the improved blood flow from the movement could improve your cognitive skills and maybe being forced into a 3D all-around situational awareness "awakens the ancestral hunter" ie.e. improves awareness, focus and concentration. A good example is driving a car. It tends to put me in a focused mode.

But, lacking that, at least having some neck movement between screens must be a good thing.