Do I know this for certain? Hells no, I have no inside knowledge.
But if you look at the WWDC video for Airplay 2 around the 35 minute mark, or look through the slides. You’ll see it’s all eerily familiar.
Personally I think that until Apple flips the switch on high-res in iTunes/Apple Music we aren’t getting it officially in Airplay 2. But, I’ve been wrong before. 1983 I think it was. Checked jeans, what was I thinking?