In beta 2, I was able to play the music stored on my watch to an Airplay device. Now only Bluetooth devices are available. Even the watch control panel on beta 3 does not list Airplay devices when tapping the “Airplay” icon.
Are you sure you were able to AirPlay from Apple Watch to HomePod? On beta 2, I was able to AirPlay from iPhone to HomePod — but not Apple Watch to HomePod.
That being said, on Apple Watch, I was able to control iPhone AirPlay settings, set iPhone to AirPlay to HomePod, and control iPhone music.
However, audio must be routed from iPhone to HomePod — I did not have any way to AirPlay directly from Apple Watch to HomePod. Functionality works the same in beta 3.