What I don’t understand is what the ATV4K has to do with “supporting” sample rates greater than 48kHz anyway… it has no analog outputs. All it needs to do is pass the HD digital audio bits along to the next HDMI device so that when it eventually gets rendered it comes through with all that high res goodness (that most of us can’t discern from 48kHz anyway through our merely decent speakers :-).
Personally, I feel this gripe is much ado about very little. If I’m listening to AirPlay speakers I know they’re receiving/rendering any 96 or 192kHz 24-bit source at no more than 48kHz. Likewise, if I’m listening with the world’s best Bluetooth headphones — 48kHz max!
In the case of high-end HDMI receivers and soundbars that support truly high res (and truly rare as of today) 96/192kHz audio streams, I do question why the ATV4K doesn’t simply pass the bits through in their original state… I suspect there’s a reasonable explanation that’s beyond my level of knowledge. Speaking of my lack of detailed knowledge about all this, here’s a good relevant article by a guy who knows a lot more than I do.