I think it's too early to be projecting who does what although I agree with @xwalker on the best guess now. As for McClain coming out after one down, I wouldn't think that'd be the case. He may rotate out in the nickel some but none of the best rushers are going to always be on the field at the same time all the time on passing downs. I could be wrong and Melton could end up with well over 70% of the snaps. My guess is he won't. Also keep in mind we often use both our DTs as 3s esp in the nickel. We had some problems with that when we lost our LBers esp Lee as opponents would split the 3s and run thru it. And around it and off the strong side over Selvie. You should see better pressure with better run support assuming we can stay healthy at LBer.