Ron Rivera was a finalist earlier this year in Pittsburgh's search for a new coach. As you know, the Steelers run the 3-4, so naturally I thought the question of what he would do with the defense had to of come up. I did a quick Google News search, and came up with this article from a Pittsburgh paper:
He has used a 4-3 alignment with the Bears since taking over as the team's defensive coordinator in 2004. The Steelers, meanwhile, have long employed a 3-4 look and constructed their roster to fit the needs of such a defense.
"Would I come in and blow everything up just for the sake of doing it because this is my initial plan? No, you can't do that," Rivera said. "You can't ask the player personnel department to all of the sudden scrap all of the players you have and try and find everything to fit automatically. In Pittsburgh, you look at the players they have and it would almost be like trying to put a round peg in a square hole. You just can't do that."
Kind of vague, it sounds like he would try it, but if it didn't work, he would be working his way back to the 4-3. I can't find any other specific references to the 3-4 by Rivera, I'm still looking.