It isn't so much 1 shot, its kill pressure. Can they kill you with one rotation and at what hp is it possible. Zed and Talon are well known for their high kill pressure because they can 100-0 you in one skill rotation at level 2-3, as can Kat and several others within the assassin/adc/toplane group. Mages were rarely able to accomplish this so instead had ways to stop this from happening, as did tanks and supports. Now mages are about to be dead, tanks get wrecked early, and supports are the only ones left able to prevent this (against enemy adcs).
This means that champions with more kill pressure are becoming increasingly popular and only those that can mimic it will survive. Mages will take electrocute to achieve this as many already are (Syndra, Malz, Lissandra) or suffer the consequences. Tanks will sit under towers waiting for ganks or switch out for top-lane carries like Quinn and Kennen (I've seen so many more Quinn and Kennen toplanes recently), and supports will stop trying to mitigate damage (tanks like Braum and Taric or enchanters like Janna and Saroka), and instead aim do damage themselves (Lux, Zyra, Annie).
In short someone is going to get fed, someone is going to feed, and jungle is going to be the deciding factor for the game. At that point snowball champions will naturally be best which means expect assassin's and adc's everywhere in every game (seen jhin and kai'sa midlane several times in the last two days).