Vilma should be perfectly capable of playing a 3-4 MLB.
He's not big or strong enough. He's a fantastic athlete but the holes in his game definitely fall into his responsibilities as an inside guy in a 3-4 D. He struggles shedding blocks, and playing in traffic.
When he can fly to the ball and get out in coverage, he's excellent, but when he's gotta deal with Guards or fullbacks coming at him he definitely struggles and always has. I think this change probably spells the end of him in New Orleans, which is a shame because he's one of my favorites.