1. Its a lot easier to adapt the schemes to the personal than the opposite.
2. There were rumors the Ravens wanted to go back to more of a 4-3 type and the 4-3 Under looks a bit like the 3-4 but serve their player they have right now better. This would let Suggs rush the passer and not drop in coverage as much as he's getting older.
3. The way they drafted players. Sure you can say most of them are versatile enough to play both the 3-4 and 4-3. But in my opinion, Correa isn't strong enough to play the 3-4 position yet and face NFL OTs on a regular basis and still set the edge. In the 4-3 Under, he would be most of the time facing the TE. He would still rush the passer, but also use his speed to drop in zone as well and blitz from multiple positions. Kaufusi is another exemple, right now I know he's at 285 but he lacks a bit the power to play DE in a 3-4 schemes. He Bends very well and play very well the 4-3 DE position. He could be a role similar to Chris Long had with the Rams, bigger than Quinn so taking the OT and letting the SAM (Correa) a clear path to the TE or RBs in pass blocking. The 4-3 would also give Jernigan a very good season. He's a 1-gap type of guy and playing the 3-tech in a 4-3 might be the best thing for him. He will be a beast getting in the backfield a lot. Henry is another player that would fit best in that role on passing situations. If there were to give A. Brown one last shot, the 4-3 Weak Side LB is ideal for him.
4. There were also rumors the Ravens are going to run some more Tampa 2 schemes with the addition of Leslie Frazier. Having a very good front 4 is ideal for that type of schemes if you want to make plays. Young is a perfect fit for a zone scheme imo. He attacks and tracks the ball very well in the air. A ferrocious front 4 (with some blitzing LB (Correa- Mosley) will help the secondary a lot. Why do you think the Panthers let Norman go ? Zone corners aren't as valuable as man corner in a 4-3 zome schemes. THe pass rush is the key to the Panthers.
5. I mean that is just what I would do if I was the Ravens D coach. They have all the talent to play the 4-3 right now. Sure the 4-3 Will LB position is a bit unknown right now (thats why I wanted to Ravens to draft 1- Cravens, 2- Vigil 3, Jatavius Brown). They need to add speed to the LBs to cover the TEs/RBs what killed us last year. They could add a training camp cut, maybe move Weddle in the box in a BIG 3 safeties schemes and Brooks/Webb in deep zones. Weddle is very good at covering the hook zones, TEs, RBs. I mean its not a true 4-3 because in todays NFL you need to add speed, and the Will LB is more of a safety who can play the run pretty good.