I disagree with you here.
I have a Thrustmaster TCA Boeing throttle quadrant, which has reverse levers that, when lifted, HOLD a button down. Therefore, they are meant to work with the “HOLD THROTTLE REVERSE THRUST” keybind.
That has never worked on the ATR – not in the original release and not in the currently available release.
EDIT: Let me add, too, that I hear an audible click when I activate HOLD THROTTLE REVERSE THRUST via the levers on my throttle quadrant. However, the reverse levers on the throttles in the sim remain in the forward thrust position and when I move the throttles on my quadrant the throttles in the sim go forward rather than backward.
See: