Ok, so here's the scoop: The United States Department of Transportation’s Federal Motor Vehicle Safety Standards for lamps and associated equipment require that all turn signals (front or back, it does not matter) must be at least 2,200 square millimeters in size. The 2,200 square millimeter measurement doesn’t apply to the turn signal as a whole, but rather every single section that lights up in a row. So you can have sequential turn signals on front or back or both, as long as each section of the sequential turn signal meets the 2200 square millimeter minimum size. The Mustang’s signals get a pass because each segment of that turn signal is larger than 2,200 square millimeters.
My guess is the new K900's will NOT pass, because it does not look like each segment of the sequential turn signal would equate to 2200 square millimeters (which is really not as big as it sounds).