But even on the web there is limited ability for applications to share data without explicitly working with the apis. A central filesystem allows for "star network" integration rather than point-to-point
The API is already there: it's HTTP. read() is GET, write() is PUT or PATCH, unlink() is DELETE. If you want to be fancy you can use WebDAV, which is also a standard API.
You don't need APIs, you need standard file formats, just like with filesystems.
Its just a different kind of addressing. The way different things are integrated is an independent concept.
Perhaps you could expose URLs in a unix file model style and pretend that they are files. Or build http into the kernel and give every file and executable on the system a URI. Or even map 64 bit processor address space to IPv6 addresses. Based on a 4k block size you could address every hard drive in the world in a 64 bit single subnet.
My point is that files are just one type of abstraction. URLs are just better.
