I doubt this even saves pennies. These lights are driven by an IC, and the current is regulated because the supply voltage is nowhere near stable enough to get

I doubt this even saves pennies. These lights are driven by an IC, and the current is regulated because the supply voltage is nowhere near stable enough to get away with an unregulated drive circuit. The mention of the TLE4242 chip upthread quite clearly indicates that there’s an entire wire from the ECU to the driver to control it. All that’s needed is for the IC to support some way to change the current regulator set point instead of flashing the LED. Sure, this would add a handful of transistors and maybe a capacitor or two inside the IC, and it will cost some R&D, but it won’t affect the unit cost in any meaningful way. (This could be as simple as a filter that turns the duty cycle into a current target. This feature is nearly ubiquitous in off-the-shelf “dimmable constant current” line-voltage-input LED drivers from basically every supplier (e.g. Mean Well). The tricky bit would be to get the thing to turn on quickly enough without annoying brightness swings, so some actual care in the filter design and frequency selection would be required. Or one could use 0-10V control (also ubiquitous) or have just two states plus off or have digital control… there’s no shortage of perfectly fine solutions.)