Trading Turris for a winger makes a lot of sense, but I'm not convinced Kovalchuk is the answer.
He seems like a guy who rather pops a can of Pepsi than work harder if he's relegated to 3rd line.
I'm not really sure where you are getting your perceptions from, but he's been playing everywhere from the 2nd to the 4th line all season without complaint. And regardless of whether he's in the lineup or not, he is a gym rat that is always in the workout room and skating after everyone else.
When he was given the opportunity to slam the team for the healthy scratch through the media he declined. He instead told them that his role as a player is to be ready to re-enter the lineup at any time and prove that he belongs on the ice with his play.
There have been many observations made throughout the year from media, broadcast team, and other sources that his issue is more about his playing style not fitting into the structured system that the team is trying to employ. Kovalchuk is playing as a rover that looks for any openings to attack the net and that makes it hard to anticipate where he is, where he's going, or what path on the ice he's going to take to get there.
That drawback affects both the coaching staff as well as the teammates out on the ice with him.
His style of play, which he doesn't seem to want to change, is just way too difficult to integrate into a scheme where everybody is trying to be on the same page and employ a meat and potato, north-south offense.