I love Nocturne, I really do. As much as I would be happy to see him buffed, you need a good reason for it, not "He's never had one." That's a REALLY dumb reason to buff a Champion, and you should realize that. Nocturne is in a decent spot right now, not really in need of a buff. He's not a big LCS pick, but he's not a bad Champion. He's solidly "pretty good".
He is not in a decent spot right now. He hasn't been in a decent spot in a long time. He is my favorite champion, and I can't stomach playing him these days. Mained him in Season 2.
Sure he has very high success rate on his lvl 6 gank. That is pretty much the only thing he has going for him. He is basically a severely weakened udyr that is harder to escape from, but can't escape as easily.
Problems
-His fear is too short for how much conterplay it has.
-His lvl 1 ult could be stronger, and his ult isn't nearly as strong later in the game.
-His Q should do a little more. Maybe higher speed while on it. Maybe tenacity.
-His W's power budget is wonky. He shouldn't have power budget wasted on the att speed increase. It is mostly used to destroy an incoming skill shot when you are not even in melee range to use the att speed.
-His passive isn't bad, but I think it could be better. Maybe a 1 sec shorter CD. Maybe a speed boost.