I voted for Nocturne because, based on the champion descriptions in the poll, Nocturne seemed like the choice that Riot has the best vision for how to improve him. He lacks subtlety for being shadow-stalker, and it seemed like Riot wants to focus on giving him depth in a rework.
Right now, he's just a dive bomber who is super frustrating to play against and quickly becomes boring to play as. He's one of the two champions in the rework poll that I actually play a decent amount of (the other being Fiddlesticks) but I don't even even enjoy most of Nocturne's kit. The only part of his current kit I find very interesting is the global vision denial aspect of his ultimate. His E is okayish too, but the rest of his kit is very boring and too inflexible.
I want more specialization in Nocturne's niche of denying the enemies vision, and more nightmare illusions, and less low counterplay "press R" 1-shot potential. I want Nocturne's Q to reveal hidden units so that he can use it to clear wards. I want a brand new from scratch passive and W. I want his E tweaked to be more interesting. I his R to make everyone on the enemy team hallucinate that he is diving them to cause them to panic, and I want him to have more cooldown refunded if he doesn't dive anyone so that he can ult more often for mindgames and vision denial.
I want him to deal less damage so that can't burst down a full health target. Maybe his new W can provide him an option to slip away into the shadows to escape after an assassination attempt so that he can have a less reliable assassination success rate without just feeding as a result of his failures. He could have the best target access for finishing off fleeing opponents and good vision-denial utility, but the lowest burst damage of all assassins as part of his identity. He could be a very slippery champion and always a looming threat no matter where you try to hide, but with less brute force than most champions.