The BMW X6 has been blurring the lines of SUV and sports car since its introduction in 2008. Things got even more strange when BMW threw a diesel engine under its hood and slapped an M badge on the side. Yes, BMW makes a diesel-powered M product. Unfortunately for those in the United States, the X6 M50d has been unobtainable. That trend sadly continues as the X6 rolls into its second generation for 2015.