It’s a diesel, hybrid, a plug-in, a three-cylinder – and a tour de force, perhaps? BMW’s Vision EfficientDynamics concept has been the subject of rumor and innuendo for weeks, but now the German car company is setting the stage for its 2009 Frankfurt Auto Show display with new details of its concept. As the name implies, this concept car grafts fashionable green technology on the body of a 2+2 sports car. The promise: BMW M-car performance from a vehicle with a three-cylinder diesel plug-in hybrid powertrain.What are your thoughts? Is the car too sporty and thereby (even despite its efficiency) impractical? What could buyers expect from the pricetag of a vehicle such as this? Would you drive one?GO!