Leslie Frazier and Joe Cullen were both brought in from the Tampa Bay Buccaneers to coach the secondary and the defensive line respectively. Frazier's addition has been talked about. He was the coordinator in Tampa Bay and in Minnesota in both instances ran a 4-3 base front.
Joe Cullen is the addition that really makes one think. Coming over from a team who ran gap shooting principles leads me to thing it is likely the Ravens will employ some, if not most of their concepts.
The Ravens have the personnel to run a 4-3, though a few tweaks would be needed in certain positions. Suggs and Dummervil would no longer be asked to cover. Jernigan could focus on what he was brought in to do, that being penetrating the backfield and Brandon Williams could use his unmatched combination of quickness and strength at the one technique.
Defensive end and linebacker would be the position that would need addressing. All of a sudden, the prospect of Joey Bosa manning the strong side and sliding inside on passing downs becomes a lot more attractive. Myles Jack handling Will or Sam linebacker duties would also fit in nicely, but it is easy to assume that Steve Biscotti, a self proclaimed "pass rush guy" would be enticed by a four man rush of Dummervil-Bosa-Jernigan-Suggs.
A move to 4-3 seems so likely it is becoming assumed. The MMQB's Andy Benoit, who watches more NFL tape then anyone in the business seems convinced of it, as said on this week's edition of the MMQB's podcast.
This is a move that would match personnel to scheme, and would be a step in the right direction, in getting the Ravens defensive playing at a hundred miles an hour.