From an interview with Cheryl Pilcher, Chevrolet Camaro product manager, posted on Automobilemag.com:
Will there be a Z28 model?
CP: "There will be no Z28 model. Through the four generations of Camaro, there have been cases where Chevrolet chose to make the Z28 the top dog or the SS the top dog. As you're aware, Chevrolet is encouraging the SS strategy with cars such as the HHR SS and Cobalt SS. Consistent with this strategy, we have a Camaro SS."