MacOS doesn't support stereo airplay over Homepods outside of iTunes. Read his question before you answer.
[doublepost=1546319697][/doublepost]To better answer your question: I see no reason why it shouldn't be implemented system wide. Stereo playback works via bluetooth so why not Airplay. It wouldn't be perfect especially if you're editing video (synch issues) but for Youtube and general web viewing it would be adequate. The question is if Apple sees it as a viable thing to implement. Unfortunately they have positioned the Homepod as a stand alone device aimed more at iOS users than Mac. This is short sided because of how well the Homepods function in stereo mode.
iOS already supports stereo HomePod for audio from any app (music, youtube, websites, etc.) without any problems. The reason why we don't have proper stereo HomePod support in macOS is simply because of Apple's neglect, not because of any technical reason.
Now with iTunes going away in the next version of macOS, wonder if they'll keep the stereo HomePod "feature" somewhere?
Here we are late August 2019 and still no Mac HomePod stereo support, would be nice to watch netflix with these two great sounding home pods I own working in stereo.... bummer 🙁