In theory, AirPlay 2 should come to macOS High Sierra. Problem is, we are still without any news, and we already have the first beta of 10.13.6... Also, my MacBook is not supported by macOS Mojave, as a lot of Macs out there from 2009 to 2011. So all of this Macs, that could support Airplay 2 (and, thus, having the potential to purchase a HomePod), will be left out, and probably won't invest in a AirPlay 2 ecosystem.
Apple should support AirPlay 2 on High Sierra as was announced. But I'm not sure they will.