Well, just having most all of them back should allow for improvement. Schemes and techniques will be different too. Burnham talked during the spring about how they are teaching the interior guys to shoot gaps instead of take on the linemen and go to certain spots on the field. Same with the ends. Defense will be improved big time over last year, just based on the fact that we have a real defensive coordinator whose got a long, experienced history in high D1 programs as opposed to a bunch of inexperienced, young and unproven good ol' boys.
The collegefootballnews.com preview that was posted recently on here even says we should see sack production improve dramatically.
Now, I'm not expecting all of this, or even drinking much kool-aid, as I won't expect anything until I see a few games, but I am not as worried about our defense as a lot of other fans right now.