So the Wall Street Journal said CBS in on-board with YouTube Unplugged, and Fox and ABC/Disney are not far behind. The service should launch in early 2017.
Maybe Google is waiting to announce another Nexus Player-type device from them officially until it's ready to roll out? Complete speculation on my part, but it would make sense...
You'd expect that whatever live channels that are offered via the Unplugged app/service would also be accessible via Google's Live Channels app on Android TV (where they can sit alongside other streaming and tuner-received live channels). But then again, I'm not sure we can expect that kind of logical coordination from Google...