Guys don't develop good hands. They either have them or they don't. Nichushkin doesn't have good hands. You can go back to his draft hype video where you can see him score every goal by pushing the puck around a goalie along the ice using his long reach. Pretty cool stuff, but it doesn't work at all in the NHL.
I think it's more a knock on his hockey sense.
If you're exposed to the same situation enough, you'll learn to adapt. Yeah, Nichushkin has had a lot of close opportunities where he should elevate it but I don't think he's adapted his game.
If he played more non-NHL games, my hypothesis is that he'd have a ton of in game breakaway opportunities where he could round out his breakaway move(s).
You can develop any trait. It just takes time and in game experience.