

There's clearly no technical limitation - they already support devices close enough that people can sideload to get the service running on Android TV devices. Now a different question is whether DirecTV Stream should be available on Android TV devices? That answer seems like a "yes". They could have just called it Google TV (or Google TV with Chromecast), but they didn't. Google, for their own marketing purposes, reused the Chromecast name for a different class of device (one that is a full streamer able to run apps and competing with Roku or FireTV, rather than just half of a streamer like the original Chromecast is). I don't really see anything deceptive there on AT&T/DirecTV's part. It doesn't say they support Chromecast with Google TV (or any other Android TV device), though it does when treating them as Chromecast devices. The web page says they support Chromecast, which it does.
