We've seen the following trends in recruiting since Hoke (and Mattison) arrived:
- Heavy numbers at LB.
- Low numbers at DT.
- DE that project better to a 3-man front or as linebackers. (This is debatable but bear with me...)
Furthermore, Mattison is coming off successfuly running the Ravens' 3-4 [edit: really it was a hybrid with multiple looks] and is using that fact to sell recruits. Add it up and you see circumstantial evidence that could point towards Michigan moving to a base 3-4 defense within the next few seasons (obviously not yet).
LB: When Hoke was announced as head coach, the 2011 recruiting class added 2 more LB recruits (to the 2 already committed) - a surprising number given the quantity of players returning from the 2009 and 2010 classes.
For 2012, LB seemed to be a minor need, but the coaches have taken 4 more commitments anyway.
DT: The critical recruiting need for the 2012 defensive class seemed, at least to most fans, to be for several 'true' DTs to a) replace Mike Martin and b) provide a talent infusion where no proven players return. Despite the need, it's rumored that the coaching staff is only taking one player for the position in 2012.
DEs who might be DTs: The 2011 class included the late addition of Keith Heitzman, an SDE type who some project to DT. Chris Rock had a similar profile and was already committed to the class. Previous recruits like Wilkins and Black were also thought to be potential DTs at some point. In 2012 we've seen a number of similar DE recruits - larger players who could be moved inside like Strobel, Godin, and Wormley (who is not part of the class but remains a target and, to many, a likely commit). These type of versatile linemen are generally considered to be prototypical fits for a 3-4 DE (e.g. 6'6 290 lb JJ Watt).
DEs who might be LBs: DE recruiting under Hoke has included three players weighing in the neighborhood of 220 lbs (Ojemudia, Brown, and Beyer). This is light even for a LB at the college level. Brown and Beyer are tall, but Ojemudia is indisputably LB-sized and has been quoted as saying he's a linebacker. Some of the DL recruits have been told they're seen as a 'Terrell Suggs' type player. Suggs is a LB, at least technically.
. . One can easily make numerous arguments to rationalize all of the evidence above: The 4-3 under personnel isn't necessarily dissimilar from a 3-4 defenses; Mattison's run both defenses; staff wasn't impressed with the returning LB talent; the DT and SDE positions can be secured by a variety of players; the 4-3 WDE and 3-4 RLB are roughly the same thing (e.g. Woodley); etc. ...However, as the circumstantial evidence mounts, the hypothesis begins to look more feasible. The rumor that the staff will take only O'Brien or Pipkins, but not both, seems particularly curious if the plan is to stick with a 4-man front.
This was discussed before to some degree http://mgoblog.com/category/post-type/3-4-defense but we've seen a lot change in recruiting over the last couple months.