The biggest thing is that Safety is the most mentally intensive spot on Pelini's defense, and that's what has held people back from playing. I think Pelini is going to look at how he's run things up to this point and change things. He's lost too many of his older and more experienced to not change. We are going to see the younger, more athletic guys play because of necessity.
Also who on defense has been underutilized? After 2010, Courtney Osbourne ended up having trouble with concussions and other injuries. Martin had trouble with the mental aspects of being a LB, so was moved to DE and excelled.
The biggest problem that Pelini has had in player management is that his first few recruiting classes were short on game changers. He got a number of good starters and quality men, but outside of Rex, Baker, and Martin, who was more than just a solid contributor?