Worlds will be played on patch 6.18, which is not the one we are currently playing on.
Besides Yorick rework and Kled there are a lot of things in this patch and in the previous ones that didn’t see competitive play (playoffs for EU and NA were played on 6.15), especially regarding midlane.
Just by scrolling the patch notes, we immediately see that there are big nerfs for Vladimir and Taliyah, two of the most played champions throughout the summer. This opens up the midlane for a lot of other picks that were niched by these two giants.
Aurelion Sol is the biggest contender for a prime spot at worlds, with his unmatched roaming potential (Taliyah ult is still an ult), CC and sustained damage (he also got toned down in 6.19, Riot is already keeping him on the radar). I would even dare to call him out to be the highest banrate champion at worlds (maybe together with Kled).
Cassiopeia (also nerfed in 6.19) was pretty strong even before the other guys were nerfed so she is not gonna lose her spot anytime soon, the same can be said for Anivia. Talking about control mages, Syndra is in a pretty good spot right now and she has one of the strongest lane presences in the game.
Viktor , after being nerfed in patch 6.16, is still viable but may be outclassed as teamfight mage by Orianna which received some small but useful buffs to her ult. Ryze is going to be the big question mark on whether the teams deem him worth to be played or not. Malzahar could pop up every once in a while but he is not going be a priority pick for anyone.
This year doesn’t seem to be good for a Zed/Talon meta like season’s four Worlds was, but there are a couple of guys that are in a pretty good spot. Kassadin emerged (once again) recently as a power-pick against AP midlaners, a niche in which he is the best champion in the League and even with Teleport being weaker the Void Walker will surely make his appearance on the rift.
He is not going to be blind-picked a lot anyway because he struggles a lot against AD midlaners. The only other assassin that is going to be picked in a large number of games is LeBlanc because of her flexibility and being able to bully basically every other champion. Zed is almost guaranteed to make at least an appearance but he does not look very strong at the moment.
Varus has been a good pick for almost a year without getting any nerfs, and he does pretty well in every matchup discussed up until now. Jayce got a huge buff in 6.17 and he is probably one of the best midlaners at the moment. He has a huge snowball potential in midlane and he is very good at taking towers, a factor not to be overlooked in a meta where “first brick” is so important. Gangplank got hit pretty hard in 6.16 but he still has some good matchups in the toplane so we will probably see again one of the kings of last year’s worlds.
The dark horses
The champion pool for midlane looks to be one of the widest ever just by looking at the patch notes and without even considering the pocket picks that may come out by some players, like Westdoor’s Fizz and Twisted Fate (which is going to be in a pretty good spot if Aurelion Sol is permaban) or Perkz’ Ekko. And don’t forget that Faker may just pull out a random Olaf in the midlane.