If a file system implements lock/unlock functions precisely to the spec, it should be fully consistent for the file/directory that is being locked. Does not matter if the file system is local or remote.

In other words, it's not the author's problem. It's the problem of a particular storage that may decide to throw the spec out of the window. But even in an eventually consistent file system, the manufacturer is better off ensuring that the locking semantics is fully consistent as per the spec.