BeOS got it right with BeFS. An Email client was just a folder. MP3s could be sorted and filtered in the file system. https://news.ycombinator.com/item?id=12309686
There was no query language for updating files, or even inspecting anything about a file that was not published in the EAs (or implicitly do as with adapters), there were no multi-file transactions, no joins, nothing. Just rich metadata support in the FS.
However, I think it is reasonable to think that with way more time and money, these things would meet up. Think about it as digging a tunnel from both sides of the mountain.
Whenever we're talking about interfaces, coordination success or failure is the name of the game.
Directories are a shitty underpowered way to organize data?
No good transactions
Conflation of different needs such as atomic replace vs log-structured
I would like to use a better database instead.