Cowher didn't change anything when he got there. Chuck Noll switched from the 4-3 to the 3-4 in 1982. The Steelers had a 3-4 defense for the 10 seasons prior to Bill Cowher's first year as head coach.
I'd like to see more of a hybrid defense. We have the personnel to play both fronts so why not utilize it and make it tougher for offenses to prepare?