Apple has released iTunes 12.8.2, an update for users who have not updated to Mojave (macOS 10.14).
If you don’t see it in the App Store app, here is a link to a stand-alone version.
It apparently fixes some issues with AirPlay and, of course, makes the obligatory performance enhancements, and so on.
Apple has released iTunes 12.8 (build 188.8.131.52). Other than initial support for AirPlay 2, I haven’t encountered any other significant changes. (ICYDK, the betas of macOS 10.14 install iTunes 12.9.)
Apple also released macOS 10.13.6 with AirPlay 2 support among the changes.