What is the point of going from 3-5-2 to 4-3-1-2? First of all, you have more defenders and more width in the 3-5-2 while keeping your midfield and 2 strikers. And honestly unless we get somebody like Mata or Pjanic as our new trequartista the formation adds nothing at all.
And as baggio said, its too narrow. If we think we're relying way too much on our midfield for offense imagine what happens when we switch to this formation.