The four-door sedan body style seems to be in the middle of an evolution. Once the cornerstone of almost every automaker’s lineup, sedan sales are in decline, while alternative interpretations are popping up at an ever-increasing rate. One of the more popular developments is the luxury four-door coupe, a style that promises the rear-seat comfort and enhanced accessibility expected of a traditional four-door, plus the fashionable cut of a fastback profile. Mercedes is a bit of trendsetter in this arena, debuting the CLS as early as 2004, and the German competition has followed suit with the likes of the Audi RS7, BMW M6 Gran Coupe, and Porsche Panamera. Currently in its second generation, the go-faster AMG CLS 63 is ripe for an update, but the question is this – what’ll it look like? To find out, we did a few thought experiments and put together a rendering. This is the result.