The strong point of plan9 is the universal IPC. This kills the need for a separate clients and servers that communicate with their own protocols to get access to remote resource. You can simply import / export anything, this isn't limited to static content as daemons can also export virtual resources. It also makes lots of programs unnecessary as traditional shell tools can access and modify resources and even system settings. Sort of like sysfs on linux but more on steroids.

Plan9 was also far ahead with sandboxing by having namespaces, which means you can expose restricted views of the "filesystem" to each process. Since in plan9 there's no ioctls and every resource access is simply read/write syscall (even networking!), restricting the "filesystem" is all you need to restrict what a process can do on your system.