I haven't heard anything about a re-design, so until someone links a direct statement from Riot assume that's just a rumor.
Basically, there were complaints about the Kai'Sa when she released, and Riot recently answered some questions where they talked about Kai'Sa's design and why they made the choices they did. Some people took Riot's statements the wrong way, and instead of hearing "we understand the concerns and agree we could have handled this better" they heard "we did this on purpose" and got all offended.
For a short TL:DR for anyone who didn't read what Riot said, Riot tried having a more normal suit design for Kai'Sa, where the neck didn't dip down anywhere near that low. Kai'Sa's design didn't get the idea across that Kai'Sa is a human in a Void suit properly, with her head being so small and the only human part of her showing. They messed around with the design a bit, found that the current idea got the human aspect across properly, and ran with it. Riot agrees they should have looked into other ideas a bit more, considering the original intent behind the champion.