The Camaro is a bigger car than a Cobalt. It's pushing a lot more wind with that big flat front end. Wasn't a concern during the first generations of Pro Stock, but it sure is now. They'd have to alter the front of it a LOT if they were going to make it work. Same thing with the Challenger, which is why we'll never see one of those in the near future. If the DID use them, they'd have to cut them down in the front so much, they'd be unrecognizable.
It been said that Chevrolet is coming out with a tudor version of the Cruze in '13. (I'm thinking I may have to get one of those. I LOVE my 4 door.!)
In fact, here's a picture of my car the day I picked it up. I happen to think the body would make a very effective pro stock shape, especially the nose. Plus, it's Chevy's hottest selling car. The Lordstown Ohio plant has been working 3 shifts to keep up with demand. I had to wait four weeks to get mine. (I wanted certain features and wasn't willing to buy it without them.)