Hi,
I know its an old thread but during my search I often missed a (final) sollution.
Its not the ultimate sollution but maybe it helps a bit
Im using WS2812b and therefore an arduino for driving the LEDs.
With it I measure the USB Vltage of on of my TVs USB Ports and stop output if it is low (TV is off).
In the next step I will create a script on the raspberry that start and stops the hyperion service depending on the USB state