What's the gain? At the tips you have to compensate for the variety of blade movement and for the means of that, exactly capture the blade tip movement. Otherwise get a pretty wobbly image. Seems terribly complicated, maybe impossible with 1970s technology.
On top of that, you have a much more exposed position, would need redesigned blades, tamper much more with the helicopters rotor system.
While you gain not one single rpm over the rotor head. So what's the unobvious angle here?
