In these days of MFDs and minaturisation, surely a couple of small cameras (one on the pylon facing forward and one on the cowling facing backwards, even one on each sponson facing towards the rotorhead) would be easily achievable.
If I can have sat nav and TV in my car, it must be possible to play a camera image onto an MFD.
No argument about fire etc, it would all be visible from the cockpit at the flick of a switch.
As for HUMS alerts to the crew.....that is a very complicated subject. The risk of the wrong reaction to a spurious warning (it could just be a malfunctioning sensor) is a major concern. Personally, I wouldn't like to have it but I would like a camera.