But what I want is different:
I want a universial "DB for binary files" where I can store binary data and all its metadata.
Then I can use this DB to build a app for picture galleries, music collections and tons of other things.
This DB should also support:
* automatic checksumming so that I can detect data corruption
* Some sort of version history so that I can store multiple versions of a file
* there could be built-in replication which I can use to see the same data (or parts of it) on all my devices
Plenty of applications do just this today by using the file system plus an index in SQLite. Is that method insufficient?
Then you answered your own question: "Plenty of applications do just this today".
So yes, it is a common enough case that it could/should be built into the OS.
Photo albums wants to do face recognition. Music player wants BPM detection. Should those be done by OS? I do not think so.