There are no new known features in this release cycle, as Apple has turned to development of tvOS 12.
You updated to iOS 11.4 on your iPhone or iPad, tvOS 11.4 on your Apple TV, and HomePod 11.4 on your HomePod so you have AirPlay 2 support. Now you need to assign rooms to your speakers so you can control where you’re playing music. Here’s how.
Rounding out Apple’s AirPlay 2 update trifecta is tvOS 11.4. The update adds support for AirPlay 2, and lets you use target speakers with your AirPlay setup.