Maybe a wiper right in the middle of an air channel would have a significant effect on drag?The justification of not having a rear wiper was that the airflow from the scoop flowed over the car (faster because of he scoop) and it pushed water off the rear window (no idea how that works in stop and go traffic in a snowstorm, but that was their story at least). If they got rid of that feature, they'd not have an argument (other than being cheap) to not have a rear wiper.