@whoknows idont,
I would think you would get a better view from the rotor tips as compare to the rotor head, at least being able to view beneath the aircraft for a full 3D picture even back to the fuselage itself.
You and I both wonder why it hasn't been brought to market. I believe it was about 20 years ago and I remember reading an article in Rotor magazine about technology to make flying at low levels safer. It involved cameras located all about the craft, live wire detection systems and so forth and all made perfectly logical sense. The rotor itself offers a perfect antennae and EO platform providing a 3D 360* view.
It could also be a liability concern, one entity responsible for the rotor itself, another for the radar then yet another for EO but all contained within one blade. So who do you sue if something goes wrong and your aircraft turns into a land dart or the rotor lops someone's head off?