> They are used extensively in [...] Windows itself. ADS underpins pretty much every FS operation on windows, including listing directories.
I think you might be confusing alternate data streams with NTFS attributes (not to be confused with file attributes or extended attributes). i.e. Paths are formatted as \PARENT\NAME:STREAM:$ATTRIBUTE and I think you're thinking about the :$ATTRIBUTE portion (like $DATA, $INDEX_ALLOCATION, etc.) rather than the :ADS portion, because as far as I know Windows does not use ADS extensively by any means. I've only seen a handful of uses in the OS. Or maybe you mean the fact that directory $INDEX_ROOT and $INDEX_ALLOCATION attributes are used with a stream called $I30, but I don't see why that's "underpinning" anything in any way... they could just drop the ability to create any other streams and it wouldn't affect this.
ADS underpins pretty much every FS operation on windows, including listing directories. MacOS has something similar.