I thought so too, but it turns out mu-so only supports AirPlay, but not also Google Cast, even though it supports Spotify Connect and Tidal. I suspect it might have something to do with it also being sold in Apple stores (pure speculation).
Sonos it seems also doesn't have support for Cast. Not really an issue since I don't have any of their speakers; but they are the most popular brand, so it's going to be an issue for a lot of people expecting to be able to stream to them from a Google Home device.
Sonos it seems also doesn't have support for Cast. Not really an issue since I don't have any of their speakers; but they are the most popular brand, so it's going to be an issue for a lot of people expecting to be able to stream to them from a Google Home device.