It seems like this is more of a glue layer between a more interesting backend service (EFS) and clients, but I don't know that I'd expect Amazon to do something

It seems like this is more of a glue layer between a more interesting backend service (EFS) and clients, but I don't know that I'd expect Amazon to do something like write a native client, versus just probably improving the NFS client behavior on Windows/Linux/... The neat trick would be if NFS 4.X grew support for communicating interesting operations like snapshotting.