Not sure if this was a feature in previous beta versions of Nougat (or even in Marshmallow), but just noticed today that long-pressing the home button (at least on the Nexus Player) will open Recent Apps, similar to pressing the right nav bar icon (the square) on phones/tablets. Also like on phones/tablets, the initial app selected is the one previous to the one you're using now (for quicker switching I suppose).
Edit: whoops. Meant home button, not hold.
It's a new feature as of Nougat. It was in previous previews too.
Pro-er-tip: If you're watching something in PiP, holding down home also gives you playback controls for that video