There are not many details out yet about the next generation Ford Mustang and less about the Shelby GT500 replacement. It is expected that the Shelby name might be dropped and it could have the GT350 badge. The Mustang has been seen tested near to the Ford SVT operation.
The car was certainly very well disguised but the prototype has a few things that make it look different form past shots of the Mustang seen before. It has wheels which fit the Shelby spec and quad exhausts when previous shots have only shown two. It also shows air intakes in the hood as well as the fenders on the front. This does nothing to add or dissuade from the rumours that the new Mustang SVT will be naturally aspirated. It looks like the rear suspension may be seeing changes too as there is some camouflage under the back of the car as well.
The pictures also show the inside of the car which has a new steering wheel with more buttons on it and dual pod instrument gauges. Past pictures taken show the 2015 Mustang driving around showing off its front, so the pieces can be started to be put together to get an idea of what it might look like.