The Steelers don't normally retire numbers as we know. However it's an unwritten rule that players will not be issued numbers such as 12, 75, etc.
Does Hines fit into that category in your mind? Being that receivers generally wear numbers in the 80's it would potentially be somewhat difficult to not give that number out in the future even if they did decide to keep it "sacred" for lack of a better term. Case in point, 88 and 82 are issued without a problem these days. Even with the trend of using numbers in the teens now being more and more prevalent.