I'm more worried about the DC. Whoever is brought in to be the OC is going to be a yes man for the HC.
Someone like a Klint Kubiak may not be a bad option if he's available.
If Johnson could get Dennis Allen as his DC ok, absolutely. However if they don't get Allen I really don't believe that they have to poach for big names.
They could be very effective by deciding whether he wants to stay with the current 4-3 or switch to a 3-4 and then look for upstart position coach that central to the defensenyour running.
If your staying with the 1 GAP 4-3, you don't necessarily need a veteran DC when you already have veteran players, especially at both the WILL/MIKE LB positions.
I would look for a quality defensive line coach like Kris Kocurek from the 49ers.
If they're moving to a 3-4 I would love to see a LB coach like Greg Manusky from the Broncos. That Broncos defense played well beyond expectations this year and an assistant like Manusky was right at the heart of that.
If they get Allen then great. Getting a DC position in the city of Chicago is probably the best job a defensive minded coach can get short of very limited HC openings for defensive coaches.
If they don't, then get a defensive line coach for DC who is going to get this front 4 up and off from its ass, as well as help identify the young defensive line prospects your looking to bring in during the offseason.