This needle valve incorporation into the head seems to be one that is being explored. The Robox 3D printer also has a needle valve incorporated into the head. Although they have as yet not fully exploited this capability they plan, like the above adjustable head, to be able to fully control the partial opening and closing of the valve. They also suggest that by partially closing the valve it would reduce the width of the extrusion path. Given that the printer is moving at the same speed but the flow rate is reduced then this would be true i.e. less material is deposited per mm. I think the issue would be that you may have less control over how the extruded material is laid down.

At the moment it is sold on the basis of being able to prevent stringing during travelling.