If a file emitted by some third party program is intended to conform to some type, yes it would be great if that type was expressed in the filesystem. Maybe that would look like a reference to a 'schema description' file that has a specific format that is bundled with the app.
Now, that doesn't stop MyProprietaryApp from declaring that the type MyProprietaryFile consists of a big bucket of bytes which it then interprets how it likes, but that's inevitable and not worth worrying about.
The point is to enable defining directory and file schemas for my OS and applications that I can control so that interaction and discovery within these systems isn't so baroque.
Now, that doesn't stop MyProprietaryApp from declaring that the type MyProprietaryFile consists of a big bucket of bytes which it then interprets how it likes, but that's inevitable and not worth worrying about.
The point is to enable defining directory and file schemas for my OS and applications that I can control so that interaction and discovery within these systems isn't so baroque.