I think the 3-4 puts us at a definite disadvantage in recruiting DLs. The recruiting pitch of we want you guys to be plugs just doesn't seem that attractive. I don't care what anyone says about last year, the pass rush just wasn't that effective, a few outsider articles have been written on BYU's lack of pass rush last year. Additionally I think the 3-4 marginalizes a huge part of BYU football and that is the big poly lineman. I am really not sold on the 3-4 being effective at BYU, I think we will continue to see the best poly D-linemen headed to utah as long as we are in the 3-4.
In terms of linebackers I don't think the 3-4 has helped us land any more talent than we would have anyways. We have enough two star OLB/SS prospects to for two teams ( no knocks on the guys, I am just saying).
Those are my thoughts, I think the 3-4 can work at the NFL level, I'll be surprised if BYU pulls it off at the college level, I anticipate a strong rush defense this year but on third and long the QB has all stinking day to throw. This strategy will work against bad teams, but if you give a QB all day to throw we are going to get scorched. I also don't like the bend don't break model of letting a team inch it's way down the field with 8 yard passes until the field shortens, good teams are going to score on you at this point.