Having the LED control exposed through the firmware completely defeats this.
There's also the scenario where the LED or the connections to it simply fail. If the circuit doesn't account for that, then boom, now your camera can function without the light being on.
Can't think of any other pitfalls, but I'm sure they exist. Personally, I'll just continue using the privacy shutter, as annoying as that is. Too bad it doesn't do anything about the mic input.
More also you'd want a hold up time for the light (few seconds at least), as taking pictures would flash them for 1/60 of a second or so.
Even so this whole attack vector isn't solved with this. How long should the light stay on for after the camera is put in standby before a user considers it a nuisance? 5 seconds? So if I turn my back for longer than that I'm out of luck anyways.
The anti-TSO means would be a hardware serial counter with a display on the camera. Each time the camera is activated the number is incremented effectively forming a camera odometer. Then if my previous value does not match the current value I know it's been activated outside of my control.