Unity just released a video showcasing the new functionality in the Unity 5.5 beta. The new Animation Window interface is aimed at improving workflow and performance. From the Unity blog:
The headline feature is the new box tool, which allows far simpler moving, scaling and even ripple editing of keyframes in your animation. In addition to this, we have carried out a host of performance improvements under the hood that should make your experience animating in Unity far smoother. We’re committed to bringing you better and better tools for animation. We’re looking forward to announcing more exciting additions to Unity for artists and animators soon!
Most critically, they included this short video demonstrating the new animation functionality.