I was surprised not to see this posted, so I pulled up the keynote again and took a pair of screenshots. In the YouTube section of the keynote, they had a part dedicated to viewing on TVs. They didn't specifically call this the Android TV app, but they did a live demo in this app using an Android TV remote. So take a look, but make of it what you will.
This looks like the same UI that is on my LG smart TV.
When the new Shield TV was released, it was stated that the new Youtube app would come when support for 360 videos is added. Since this is what Google showed off, I would assume this is the new app that is suppose to finally bring parity to the standard leanback Youtube app.
Mother of God, my body is so ready.
I do believe they also showed YouTube for kids, well I think maybe just the icon for it
Looks like the Roku app.
It definitely is going to be a new app. The keynote showed off a new app and you can see it briefly in the "What's New for Android TV" talk when they talk about YouTube's three "channels"
Its the same UI as youtube.com/tv! Its better than the current though! Me happy 😊