Currently it does not support the Chromecast since the Chrome team has yet to make an API that we can embed into our app. It sounds a bit technical, yes we know, but rest assured that as soon as we can support the Chromecast, we will.
For now, if you want to use a Chromecast to display your wall, we recommend that you install the Google Cast Chrome Browser Extension and then navigate to your wall. From there you'll be able to cast the tab that your wall is in.