My thoughts on the upcoming changes to QSS and its relation to Zed
A part of the reason why they are going through with the QSS nerf is because of the variance that Zed's assassination has. It's not as assured as for example Talon, whose only assassination requirement is a check on whether or not he has enough AD and penetration in order to accomplish it. Zed gives significantly more time to his opponent and his opponent's team than any other assassin in the game in addition to having a skillshot that comprises a majority of his damage that most ADCs with a dash or some kind of movespeed boost from their support should be able to dodge if they are not hit by hard CC, which is not a part of Zed's kit and must come from his team if he wants to assure a shuriken hit on you.
Don't get me wrong. I'm not trying to say he's not going to be stronger. He obviously is going to be a stronger champion. But his interactions with adcs post QSS nerf is not foregone in the slightest unless he's jumping on Twitch or someone equally as vulnerable. After the nerf goes through, a larger emphasis will be placed on ADCs on their positioning and when to use their mobility spells in a teamfight, especially when Zed is waiting for them to screw it up. Regardless, these are core skills ADCs should be showcasing every game anyway.
If I can make an educated estimation based on my 4+ years of playing this game, I predict that his winrate won't get that much higher in the higher elos. It might shoot up in the lower elos because of people not being as aware of him, or knowledgeable on how to peel him or how to dodge his shurikens. But either way, he won't be able to just ult on someone and spam his buttons and win. Zed has never been a champion that just does that like Leblanc or Talon. There is a great deal of thought from both parties as to how to deal with those three seconds. QSS is opting out of gameplay. Opting out of Zed should not be a fair way to play against him. You are supposed to play WITH him, just like every other recent champion in the game. Not champions like Jax, Nunu, Irelia, Yi, etc. that force you to lose to them and don't showcase their skill while doing so. And in the slim chance that he does become like those champions, despite the safety nets in his kit for his opponents present in the forms of skillshots and melee range AoE, then I'm positive he will have power taken out of his ult and made up for elsewhere in his kit, like lower cooldowns or higher ratios.