On the matter of new skins, all League of Legends champions aren't equal. It's the case for Kai'Sa. This champion has been released on March 2018 (a little more than one year ago) and has got already 3 skins (with the Prestige edition of her K/DA skin). Apparently, Riot Games think it's still not enough and have given her a new skin with the upcoming cycle, patch 9.13, alongside Caitlyn (who also boasts lots of skins), which will also get a prestige edition.
Arcade Caitlyn: 1,350 RP
Arcade Caitlyn, Prestige Edition (100 prestige points)
Arcade Kai'Sa: 1,350 RP
Written by Charlotte "Cthulhu" Rognant. Translated from French by Millenium.us.org.