Iím sure there are elements that evolved from the 4-6.
It if you watched the whole video around the six minute mark they talk about the front that Pettine added.
It really is a both simple and complex. Simple in that the formations are driven by the offensive front. Basic strong side weak side formations.
Then you add shifts, different coverages for the formations.
But one thing is a for sure it is an Attacking defense.
And there will be a lot of different looks pre snap.