Nocturne is my favorite champ and also the champ I have the most kills with. He definitely does not need a rework as his current kit is more than enough to take down many champions. I find him very fun to play in the current meta. He doesn't need huge buffs or even a gameplay rework, just something to help him be more......... Ghostly... I guess is the word. Frankly, I find all his abilities to be very good. All except for the spell shield. You would think that a spell shield on an assassin wouldn't work, but on Nocturne, it works very well. My only problem with it, is that the duration is very short and many people often mispredict when an ability will hit. To reward successful blocks, it should either... A) give him a movement speed boost in addition to doubling attack speed. This way, you can keep up to your target while getting the tether off, or B) give him protections for a short while on successful block, or C) to reflect a small percentage of damage back on a successful block, or D) allow it explode in a small radius around nocturne when it blocks an ability, dealing damage, and slowing for a short period of time.
Now, I'm all for giving him the moving through terrain with the Q, but that gives him incredible mobility in the early game, so it would have to be a passive attached to his ultimate. That way, by level 6, you can level your ult and start chasing down those pesky mobility champs.
I'm not down for increasing the range of his ult. As it is, you can still successfully gank someone that is out of position. That's what it's used for. I don't want people to start seeing it as a way of zoning. I don't want him to become Blitzkrank. Everyone is too scared to push the wave or even make a risky play like going for the dragon. Being able to ult from anywhere makes for a boring gameplay. It punishes way too easy.
Nocturne is a great overall champion that is actually in a very great spot as of now. He's fun to play and teaches everyone not to overextend. He might need a few tweaks, but I would never recommend a full rework. I want him to stay LOL's best diver.