That's pretty sweet, but it's an entire additional layer of unnecessary complexity. Plus it still requires everyone to implement a new protocol into their apps. Why not use one purpose-built for it?

Also, WebSockets bring some nontrivial complexity. This can bite you with things like proxies and custom backends, which have to implement a special code path from normal HTTP to handle WebSockets.

I basically view WebDAV as the weird one off protocol here. 9p runs over just about any stream oriented transport (including web technologies), while WebDAV is planted firmly in web technologies.

Yeah... computers are hard sometimes.

If you want to read and write files, there are plenty of operating system APIs to do it super simple. If you want low level access to file systems and to get into the complex parts... well WebDAV sucks because the underlying problems of file systems suck.

But you don't need that level of complexity for large classes of problems.