Will the new Cadillac CT6 have the rakish, expressive styling of the Elmiraj show car , or will it be a conservative evolution of the luxury brand's current design language? While those questions will linger probably until the CT6 is unveiled later in 2015, AUTOMOBILE has learned this about the sedan, which uses General Motors' new Omega full-size rear-wheel-drive platform: It will have an aluminum body. The Cadillac CT6 , which will be a bit smaller than a Mercedes-Benz S-Class but larger than the midsize CTS, also will be the first to use an engine, or engines, from GM's upcoming four-/six-/eight-cylinder family.