One move that seems certain to happen is Mathias Kiwanuka moving back to DE from OLB. Kiwi has the physical ability to play linebacker, but the fact of the matter is, he's not a LB. Last season, he struggled in most games, only adding to the Giants' frustration on defense. He was occasionally used as part of DC Perry Fewell's "NASCAR" (sic) package, where seemed more at home on the line of scrimmage.
Kiwi was moved to OLB after Perry Fewell came aboard as DC in 2010. After a few seasons of Danny Clark and Keith Bulluck at the position, Fewell decided to try to fill the void with Kiwanuka after the Giants drafted Jason Pierre-Paul in the first round. Kiwi was the extra piece in the defense and they needed to creatively try to integrate him in.
By moving Kiwanuka back into DE rotation, the Giants will defray the loss of Osi Umenyiora (who has still not signed with Atlanta) behind JPP and Justin Tuck with an experienced player. Then, Adrian Tracy and Adewale Ojomo can be accepted as sufficient depth.
The LB corp will look different, but should be more efficient. Either Dan Connor or Mark Herzlich in the middle and a group consisting of Keith Rivers, Spencer Paysinger, Jacquain Williams and Jake Muasau vying for the other spots providing the Giants don't spend a high draft pick on a LB (which they rarely do).
Hopefully, the team will not have to deploy the three-safety set as much this year. With more capable LBs on the field they should be better against the run, which as we know, helps stop the pass.