Benjamin Mayo, writing for 9 to 5 Mac:
Although strangely not mentioned in Apple’s WWDC keynote, tvOS 13 beta 2 has a nice surprise: support for Picture-in-Picture video playback.
You can now watch shows from the Apple TV app whilst multitasking around the rest of the operating system. Just like the iPad, Apple TV users can leave the video playing in a thumbnail window whilst they navigate the rest of the operating system.
This seems like the sort of feature that Apple should have demoed on stage. It probably would have received a greater response than PlayStation 4 controller support did.