I was diagnosing vibrations and rescue issues recently, and such thing would help a lot.

Spirit could transmit (over telemetry) the angle between the rotor disc and the level plane. At least what spirit thinks this angle is.

So for example, if you're hovering upright, it would be around 0. If you're hovering inverted, it would be ~180. If you're in knife edge orientation, it would be ~90.

This would help with rescue issues GREATLY.
Having that, you could:
- check the angle in flight, while hovering, to know your rescue is right, instead of trying rescue at safe height (of course radio can read the value for you)
- check the angle after landing to know if vibrations caused rescue to go off track
- check the angle before takeoff to make sure you didn't screw anything while carrying the heli
- setup an alarm in the radio "if throttle gets on and rescue_angle > 5 degrees ==> alarm" (if using flexible radio, like OpenTX).