In fact, Google Play Music can cast to Sonos directly from the app. I had hoped that this capability would be extended to all Chromecast-capable apps, but it looks like this is some special thing that only the Play Music app can do. It's a shame, because the inability to use my podcast app with Sonos is the only reason I don't have a Sonos speaker in my home right now. Sonos is abysmal for podcast listening.

Dan, I'm not all that excited about that announcement. You can already cast audio to a normal Chromecast and control it from the phone (you don't need the video). The only announcement there is that they'll be working with manufacturers to remove the need for an HDMI adapter with a headphone jack.

What I'm really hoping for is for Chromecast to add Sonos-like multi-room audio. That might not be possible with current hardware, but I hope someone does it. As great as Sonos is, the Sonos app is pretty bad.