Porsche announced plans to build a hybrid version of its Cayenne SUV by the end of the decade, but didn't show an example. It will share much of its powertrain with Audi's Q7 hybrid concept--which debuted in Frankfurt--although we expect the gasoline-powered portion to be a Porsche-exclusive unit, possibly the 4.4-liter V-8. The hybrid Cayenne should exhibit a 15-percent fuel savings over regular examples.