I think we might see more younger players coming in and playing right away. Remember the kids who were recruited by BC and Company were picked to run Coz's crappy defense. Maybe Bo has been able to work with these guys and make them into the players he needs for his system. Only time will tell though!
First off recruits are not "picked to run a certain defense." In fact, unless you are USC, or Texas or Florida (and, to a lesser extent Michigan, LSU, Georgia, Ohio State) you do not "pick" any recruits --- you simply settle for what you get --- the recruit picks you. At USC everyone wants in and the coaches actually hand pick who to accept and who not to accept. When you are Nebraska (the 2004-current version) you do not pick. Instead you hope against hope that the players you want will accept you. Overwhelmingly that is not the case. So... you take who you can get. The current NU roster is filled with players that USC, LSU, Georgia, Michigan, Ohio State, Texas, Florida and a group on another say 7-8 schools would not accept. Now, true we have a few players that these programs would entertain but overwhelmingly we were not competing for these guys against the big dogs (Callahan was famous for "appearing" to compete against the big dogs --- in that he courted many who were looking at the big programs and at NU --- but almost all went elsewhere in the end).
The bottom line is not that the vast majority of the defense was recruited to play the Cosgrove defense --- rather, the vast majority of the roster consists of guys that are simply the level of players that 2nd and 3rd teir programs (like NU) can get to sign. That is, it is not an issue of not fitting well our specific defense --- it is an issue of simple athleticism --- our guys are nowhere near (as a whole) the caliber of athlete to compete with teir one talent the likes of which resides at the top 20 or so current programs.
Will there be a major turn around? I think not. A turn around yes. Once the penalties and the mental errors are eliminated the defense will improve --- likely by a good deal. But a major turn around happens only when the LB'ers are all fast, strong and quick (like those athletes at the top 20 teams) and when the DL and OL are strong, explosive, and skilled (like those at the top 20). It is when we have safeties and skill position players that are fast, quick and strong. Right now, our athletes, relative to the top tier (and even the 2nd tier) are not able to, physically speaking, compete. That will not change much next year,