Nobody ever pays attention to these reduced speed signs. Therefore, this will be the only car slowing down in the reduced speed zone.
If, as the article states, the car slows down by cutting fuel and not by applying the brakes, it will decelerate without brake lights. The yuppie texting in the BMW behind you will not expect the deceleration and rear-end you.
Slowing down by reducing gas flow is the equivalent of stepping off the gas.
If that causes a rear-ender, the fault is not with the car is in front.