Don't forget that we will not be 3-4 exclusively. I'm sure we'll be in 4-3 and even in 5-2-4 formations that will call for different personel. Being named a "starter" doesn't mean the same thing that it used to. Not with the mass substituting that teams do now.
I think this is a move to get the best group on the field for every down and distance. McCullers isnt going to be a passing down player so IMO couch will move inside on those downs. I worry about how many snaps he can give us if I am correct about his role.