My assumption is that is probably a retired image from the earlier days of sketching. Leaking info is one thing (especially in this case, which is probably an orchestrated leak), but leaking images is strictly verboten. If anyone in the design center so much as emails a confidential sketch to a non-GM email address they are fired immediately and without appeal. Although I have no idea what it looks like beyond the shot in the article, reputable design people I know are excited about it.
Me? I'm fuckin' stoked. Half a decade in Los Angeles has made me allergic to all things German and there's something keenly douchey about Ferraris, Lamborghinis, Maseratis and McLarens. Although I discovered recently that a 2006 Maserati Cambiocorsa is not out of my price range at the minute. And they have back seats. So I'm toying with the idea of waiting for the Gran Turismos to slide down that depreciation scale towards approachable. They're at, like, fifty k right now. The image I grabbed is literally the second-coolest looking one available from a google image search of "mid engine corvette." I remember seeing it before; I think it's a rendering Car&Driver commissioned a year back or so. (The coolest, of course, is the best car Chevrolet never made.)