The 9P protocol is designed to deal with arbitrary blocking, as synthetic filesystems commonly block reads until some data is present. There are also automatic reconnection proxies (aan), and when a mountpoint is entirely unresponsive (lost connectivity), you can just unmount it. The pending calls will all fail gracefully.

The abstraction works well. The main issue is when you lose access to your root device. Just like if you booted a Linux machine from NFS, the root disk connection must be stable (how do you unmount without being able to read the binary). All other mounts can be arbitrarily flakey.