I think trading Holl is a risky that could have consequences come playoff time. He is one of the guys who is willing to be physical behind the dots, which is especially valuable when playoff-style hockey emerges, the puck is deep and players are skating like a bat out of hell to drive through defenseman.
Whichever one of the two he moves (assuming Dermott or Holl), you can be certain that the difference in the cap space hits between the two is less important than Dubas, Keefe and company assessing what they believe they have a a group and shedding what they view as excess.
Now, if this is a move to free Cap space AND Dubas has his eyes on a particular upgrade in the top four by the deadline (assuming the movement of another contract and/or LTIR Cap accumulation), then it makes perfect sense. Yes, they've played well of late and they could have a good part of their future D set, but, you need a stellar top four and depth is invaluable.
I will say it again, as someone who wants to see this franchise reach the summit, I am not confident in too many young D-Men come playoffs. Certainly I want my top four to be reliable, experienced and with some necessary grit.
We know how important this element of ones D is when one of the Habs (Gallager perhaps, someone can remind me) stated after the Leafs were beaten, something to the effect "we knew we were going to win game seven once Muzzin got injured".
Muzzin brings it when the chips are down and he makes opposing teams work to get to the net.