I know that everyone is frustrated, but Buddy Nix laid the groundwork for this defense.
I don't think that a major coaching overhaul would be wise. Teams that constantly make major changes in the coaching staff most often end up on a continuous treadmill of poor results.
While I think youth and talent on the OL is the biggest problem, I would not be too surprised to see a change in OL coach. I don't expect Hackett to be fired - his hands were really tied by poor OL play, injuries at RB, mediocre QB play and inexperience at WR.