Just last week Koushik Dutta was teasing that he might have Android mirroring ready for the Chromecast soon. He must have worked hard on it all weekend, because he has already put up a video demo of the mirroring in action. While the video demo is obviously not the same thing as a release (beta or otherwise), it's still great to see that he is quite a bit closer to bringing this functionality to the public.
As an homage (or a big joke - we aren't sure which), Koush used Flappy Birds as an example of what he can mirror. You will notice there is still a bit of lag, but that is to be expected. Eventually, Koush plans on bringing this Android mirroring functionality to his AllCast app. We will keep you updated!
Source: Google+ - Koushik Dutta