UPDATE: It also looks like Apple is adding support for AirPlay 2 in this beta as tvOS 11.4 references a feature.
However, this underline (as it was before) requires a HomePod program to be on a latest beta, that is now unavailable. Attempting to emanate a stereo span will prompt that “a HomePod program refurbish is compulsory to finish stereo span setup.”
This is zero new as users got a same warning when attempting to emanate a stereo span in early iOS 11.3 betas. Hopefully, if Apple skeleton to launch this underline alongside iOS 11.4, a association will hurl out a HomePod beta to developers.
iOS 11.4 is set to entrance in June, that gives Apple during slightest dual months to exam and presumably mislay a underline entirely.