That's basically the same story of how USB BC 1.2 (the old 'battery charging' standard that allowed 5V-1.5A out of USB plugs) came to exist. Vendors were making custom protocols that allowed higher currents than the measly 500mA USB permitted, and eventually the USB-IF threw up their hands and essentially incorporated these industry-made solutions into the USB BC1.2 standard. It wouldn't surprise me if SAE releases some new standard that happens to be NACS...