Today while driving in to work, I saw a bright red M-plate (manufacturers plate) 2005 Mustang GT, with a functional "shaker" type hood scoop, mounted to the engine and protruding through the hood. I wish I had a camera handy, but I didn't. It was not a hack job, but an apparently finished part, so I am guessing it is well along in development. No other major changes were apparent.
So it looks like there is a Mach 1 version of the new Mustang coming soon.