The style has apparently been codenamed Moonshine and the flatter icons are slightly reminiscent of the recent iOS redesign.
What is interesting is that the new designs aren't exactly in keeping with Android's current guidelines for look and feel. So a major overhaul where the UI is concerned might just be coming our way.
Overall reboot or just icon tweaks?
Besides the likelihood that Android 4.5 might make an appearance, but in the meantime could a smaller refresh perhaps come our way soon?
The icons seen in the screens were from the following apps: Play Music, Books, Movies, and Games, alongside Google+, Calendar, People, Chrome, YouTube, Maps, Gmail, Hangouts, Camera, and the Play Store. That's pretty much the broad spectrum of Android stock apps already.
If you can't wait and would like to do your own look refresh, why not tweak your Android to look better than iOS?