AirPlay 2 will allow you to, for example, sync the HomePod in your kitchen with the HomePod in your upstairs loft, allowing you to enjoy the same music as you move through different areas of your home. Not only can you use AirPlay 2 to sync between multiple HomePods, but you can also sync your HomePod with other AirPlay 2-enabled devices from key manufacturers like Sonos, Bose, Denon and Libratone and many others.
According to The Verge, Siri integration allows you to also shuttle music around the house on command. So, if you're listening to music on the HomePod in your bedroom and plan to go downstairs to the den for a few hours, you can say "Siri, move music to the den" and the music will deftly transfer to the HomePod in your den.
It has been possible to stream multiple AirPlay-enabled devices in years past with a Mac computer. However, this new update allows any iOS device to achieve the same feat using the Home app. We should note that Apple is simply catching up to the rest of the field, as devices like the Amazon Echo and Google Home already support multi-room audio.
Another feature that is finally be enabled is stereo pairing for syncing two HomePods together in the same room. This feature has been promised for months, so we're happy to see that Apple is finally giving customers the option. You'll gain a true left/right speaker system, but you'll also need to fork over $349 (x2) to be able to take advantage of this setup.
iOS 11.4 will be released later today, and it is a prerequisite for enabling AirPlay 2.