Steelers love continuity. They love *the system* Colbert implemented as GM, the *way we do business*, draft prep, FA's, trades. player evaluations etc. Who knows this system better than anyone? Mike Tomlin. He's been there, done that. Elevating someone like Omar Khan or Brandon Hunt, as opposed to bringing in a new GM, will all but guarantee this Colbert/Tomlin system remains intact. With Colbert no longer here, yes, this would make Tomlin the de facto HC/GM, for all intents and purposes. Sliding in a position coach to Defensive Coordinator is a similar move. It reaffirms and re-establishes the Tomlin/Steelers system that's been developed and in place for nearly two decades.
If anything, with Colbert gone, Tomlin will be working more closely with the Rooneys, in a more direct chain of command.
Like it, love it or hate it, this organization has gone *all in* with Mike Tomlin, as the face of the franchise and the man in charge. It's never been clearer, the buck stops here, with Mike Tomlin. Nobody to point fingers at, it's all on him, good & bad.