I've talked about my philosophy on forwards before. I think you can fit forwards into four categories:
Elite - Can drive play in their teams favor.
Contributors - Can significantly contribute, improve, and strengthen a line, but can't drive it.
Dependents - Can play on a decent line and do a job on it, but is completely dependent on linemates for success.
Specialists - Can't really do much other than spot duty, preferably on the fourth line.
I believe in diminishing returns on lines. The best player matters the most, the lesser ones matter less. It's rare to get a strong line without an elite play driver, but they can get isolated if not playing with someone of their ilk or at least a solid contributor. The base line for a line would be Elite - Contributor - Dependent. Better than that, and you have a really good line. Worse than that, and it's not going to be a strength for you. This is obviously a general guideline, not a hard rule.
Now apply that to our roster. Example lineup:
Marleau - Matthews - Nylander
Hyman - Tavares - Marner
Kapanen - Kadri - Brown
Leivo - Lindholm - Gauthier
Johnsson, Ennis
If I'm a bit cautious to not over-correct due to the start of the season, this is how I see our lineup:
D - E - E
D - E - E
C - E - D
D - D - S
D, D
This illustrates why I'm so loathe to trade one of our great forwards. I expected one of Kapanen, Leivo, or Johnsson to take a step forward, but even with that happening, we basically have three pairings of forwards that can combine for a strong line. I don't see a forward group that is dominant on paper, and can afford moving players. I see one that is balanced just so with just enough good forwards to create three dangerous lines. Move any one of those pieces, and we'll likely revert to a two line team, and have a big talent under-utilized due to his linemates.
Bottom line: We really, really shouldn't want to move Kadri or Nylander. We need to strengthen our right side on defense, but we can't do it at the cost of both one of our better players and by becoming a two line team. In any such trade, we'd need a sufficiently good forward coming back as a replacement, which limits the value we have left to target a good d-man.