One of the drawbacks of CSS animation is that it's impossible to stop mid-animation, once it's fired, it keeps going until it finishes the keyframe. Playback controls are an obvious enhancement that would be great to have.
When you would add something like a stop or pause command you could so to say split the animation so the tweens stop on a certain position. Currently one has to create two animations to have one position where to stop. This could be done automatically by the animator. So when adding such a command to the timeline the animator automatically renders a second animation in the html/css. This would be a great option.
This would be great, but don't hold your breath for it. We have a lot to do before we can focus on this, but we will keep the suggestion in mind (and maybe the browser gods will take care of the problem in the meantime...).
It there any progress in this issue? Look here it looks like what we are searching for!
From what I have seen in the browsers the playState does still have some glitches with it. We are still looking into this area.