There is only one problem with that. How could the manufacturer do that with so many variables on when a controller is required? And when the SAE standard doesn't even test it?You read that wrong, I wasn't saying the manufacturer needed to provide a WDH. I'm just saying if a truck requires a brake controller to tow its rated weight then it should ship from the factory like that or the GCWR sticker should be adjusted down accordingly.
GM seems to do the best job with their door stickers, but I suspect even they don't change the GCWR if the truck is shipped without one. They all do it for payload; you put running boards or a bed liner on your truck at the factory and your payload gets bumped down.
They could declare when a WD hitch is required on the sticker because they know exactly what the hitch they installed is limited to without a WD system