Acura calls its all-new ZDX "a provocative luxury four-door sports coupe," adding that it's a "passionate getaway" vehicle designed for "a couple, their belongings, and more." The proclamation is a twist on a pitch we've heard before, yet with an even narrower segment focus. While the marketplace has come to accept the stylishly squashed Mercedes-Benz CLS, Volkswagen CC and Jaguar XF into the non-sedan segment, this new niche – pioneered by the BMW...