BYD may never earn luxury-level margins -- and that's OK.BYD (BYDDY 1.09%) has already won one of the most challenging battles in the automotive industry: scale. It sells more electric vehicles (EVs) than any other automaker in the world, controls a significant portion of its supply chain, and remains profitable despite intense price competition.But for investors, a more challenging question looms: Can BYD ever earn premium margins -- the kind that justify sustained multiple expansion over the long run?The ...