I haven't read all these words yet, but I recognize enough of them to know I have similar interests. I was excited to see https://bazil.org/2014/04/24/introducing-bazil/. Of course, now defunct.
"Bazil separates knowledge of a file from the contents of the file, letting the laptop know about all of the files, without having to store the contents of the file." Yes, it hits the nail on the head!
This approach is probably at the right level of abstraction, presenting itself as an actual filesystem that could become the default e.g. for a /home partition (computer) or a /storage/data partition (Android phone).
