There have been certain models in the past, where the Z28 was top. BUT, those were the model years when there was no SS.
Z28 is purely Camaro, but SS is just an added designation and an improvement IMO...hence the 4th gen's "Z28 SS". I think we could see one of those again.
Anything could happen, but I wouldn't count on Z28 being the Top-Dog Camaro.