Andy,
I think the "surprises", as with most Belichick surprises, don't turn out to be "surprises" with the benefit of hindsight. They turn out to be commonsense.
So approaching the "surprise" issue from a future hindsight perspective, lets look back as is if looking back after this upcoming season. We might then see:
The LB corps evolves over the course of the season. With some older guys phasing out, others phasing in. At the end of the season, I could envision that the nominal "starters" at LB will be Woods, AD, Mayo and Vrabel, weak to strong. The chief sub inside is Bru followed by Guyton, and outside is Crabel. Bruschi has played more snaps than Crabel but the trend is down. Crabel has played a lot fewer snaps, essentially providing blows for Vrabel, but the trend is Up. Mayo starts from day 1. Guyton has seen limited but nonetheless valuable snaps at ILB.
From that perspective, Woods just "naturally" matured, grew into, and gradually split reps with AD at OLB, after Pierre's three years of grooming and learning. AD spent the balance of his essentially full time snaps inside, just like he did last season. But in this case he swings, and goes inside to provide an "inside blitz" or over the middle coverage in passing situations, other wise he plays OLB.
That blitzing/zone pass coverage is usually primarily from the WILB position. Which means Mayo is force-groomed by Brushi into being the "mike man" at SILB. Thanks to the helmets, Vrabel might well share, along with Tedy, and be the de facto play caller, while Jarod learns the mental aspects of the game as well. Bruschi, Mike and Jarod appear to have the head to perform those activities. I don't know whether Gary could do the mental aspects of ther "Mike" job, Belichickl is the judge. If not he could turn out to be a pretty effective zone pass ILB as well at WILB.
Bruschi could then phase way down, or retire next offseason along with Larry. I would expect another LB heavy draft to fill in behind the newcomers, or to play if anyone slips.
Eventually Guyton and Crabel will contribute, more so next season after the rookie learning experience. Guyton as a good ILB sub, and possible starter over the years; and Crabel as a possible starter outside, especially in the SOLB position that Vrabel plays.
From that perspective Bill will have rebuilt/retooled his precious LB corps on the fly, as he has done before, and be well positioned for several seasons of good play there.