A commercial product called M-Files has actually implemented this. Until a few years ago i used it daily, and it is great. That said it was Windows only, so that was quite a big limitation.
That said, I see this as a hard thing to implement as the primary file system. It took a long time for some people to get the idea that the same document was in many different "folders" at once.
For further actions, you may consider blocking this person and/or reporting abuse
We're a place where coders share, stay up-to-date and grow their careers.
A commercial product called M-Files has actually implemented this. Until a few years ago i used it daily, and it is great. That said it was Windows only, so that was quite a big limitation.
Demonstration: youtu.be/seTjogkSApc?t=42
That said, I see this as a hard thing to implement as the primary file system. It took a long time for some people to get the idea that the same document was in many different "folders" at once.