Apple's AirPlay 2 discussion at the 2017 WWDC promised streaming support to multiple targets from an iPhone or iPad -- but initial testing seems to suggest that the feature is not currently enabled in iOS 11, tvOS 11 or both.
Following the suggestions of several forum members, and emails, AppleInsider set out to try multiple room streaming feature of iOS 11 to a pair of fourth-generation Apple TVs updated to tvOS 11. At present, there appears to be no way to either add the Apple TV to HomeKit as Apple suggested was necessary during the WWDC, nor any way to discretely select the track in Apple Music.
The procedure followed within Apple Music was to start a track playing, then click on the AirPlay button. All possible targets for AirPlay were available including an AirPlay Denon receiver, and an assortment of third-generation Apple TVs. The Apple TV units labeled "Office" and "Living Room" are fourth generation devices.
The interface presented differs from what Apple suggests it should look like in iOS 11 on the product page for the operating system.
We eliminated the Airport Extreme base stations as a possible source of problems by connecting the Apple TV set-tops to two other 802.11ac routers both wired and wirelessly, with them still not able to be selected in tandem.
All of the devices appear in iTunes in Sierra and the "gold master" of High Sierra as AirPlay streaming targets to multiple speakers -- as they should. However, this is not AirPlay 2, and the functionality has been in place in one form or another since 2010.
AppleInsider has reached out to Apple for comment, and will update accordingly.
We can't conclude with any certainty that iOS 11 has omitted AirPlay 2, as it remains possible that tvOS 11 doesn't have it implemented. Given the lack of compatible speaker hardware to examine the feature with, we won't know for sure until Apple says something about it one way or another.