For a 4-3 we need two starting DEs and two starting OLBs. For a 3-4 we need two starting OLBs, a starting ILB, and a starter somewhere on the DL. Either way you need to find four starting calibre front seven guys.
Judging by what Nix has done so far, we can expect to gain one starting calibre defender per offseason (two offseasons have yielded Barnett, Dareus, and a bunch of question marks/busts). The unit will also likely be poorly coached again.
Basically, our defense is gonna be awesome.