Remember the enemy ADC your fed Zed couldn't kill because of his healing? Or the Qiyana leaving stealth to burst your tank, only to proc Duskblade passive, and disappear again? Season 12 will put a stop to that.
Riot developers have stated, both officially, and unofficially via Reddit, that they are analyzing how and when high bursts of damage happen and are examining their effects on gameplay. The goal is to keep the game exciting with high stakes decision-making, but also ensure that fights are reasonably understandable and counterplay is still possible. It's still very early in this investigation, but the current belief is that burst kills happen too quickly and too often.
One way of doing this research is to play the game with a 20% nerf to all stats, and see if the gameplay feels healthier, alongside looking at the statistics from those games.
The problem with burst is closely tied to another problem plaguing the game, which is high healing and overall sustain that can be seen in all, currently, meta champions. Champions whose gameplay is reliant on one spell rotation are becoming obsolete, unless they are capable of killing the enemy outright with their burst, as anything less just gets healed up, making it a vicious cycle of pushing the burst meta.
Aside from that, the healing and self-sustain, in and of themselves, are a problem. Riot will nerf both in the next season, with the only question being if it will happen in one fell swoop, or if they'll spread the nerfs out to multiple patches.
In any case, we can look forward to the work the developers are doing, even if they are walking a tight rope of nerfing an overpowered mechanic or champion, and not deleting it from play. The current meta can be boiled down to fights in which either one team annihilates the other, or the other team is unkillable, which is not fun, no matter how you look at it.