[noggin]

Well we will not know until someone with the correct equiptment tests and reports on those "rare" 96k and 192k Blu-ray's.
Once there is hard data then a statement can be made.

Apple TV 4K only outputs 24-bit 48kHz (default) or 16-bit 48kHz (has to be selected in the settings).  

Thanks.

So 96k/192k DTS-HD MA and Dolby True HD won't be lossless decoded (rare use case, but relevant to those who have that content), and similarly 192k or 96k FLAC etc. stereo audio releases (popular with audiophiles) will also be downsampled to 48k.  

For the vast majority of users this will be 'good enough' - but it's worth caveating as other platforms don't have the same audio limitations.

The lack of HD Audio bitstreaming won't be a huge issue for many, but it does mean you potentially lose some metadata driven functionality (user-selectable DRC driven by Dialnorm for instance) as Kodi doesn't offer those controls within its decoder path (or does it?), so while it may be lossless for one listening use case, it doesn't offer the same functionality as bitstreaming across the board.