Michael Bay Dot Com has revealed that a Transformer will appear in TF4 as a black 2013 Lamborghini Aventador LP 700-4 Coupe. It is not specified whether or not this is an Autobot or Decepticon, but my personal guess is that it's a Decepticon.
MBDT: "Unveiling yet another surprise . . . the extraordinary and exhilarating 2013 Lamborghini Aventador LP 700-4 Coupe."