Asking Siri to "Watch [tv channel]" now goes directly to the live feed of that channel. This was announced as a tvOS 10 feature but was made available early. https://vid.me/SR36 I got a "What's New" screen when I turned on my AppleTV today. Asking Siri to watch a live channel was one of the features. This is definitely a watchOS 10 feature that was released early. It's no longer listed under tvOS 10 features on apple.com/tvos-preview/ @arn: This looks like news.
The demo video linked to is for CBS News. Doesn't work with SlingTV -- cable subscription required for it to work with a network television app... bummer
This is nothing new. It was added in tvOS 9.2. It's called "Live Tune-In": https://support.apple.com/en-us/HT204181