There are a variety of ways pNFS could be used in currently released OpenStack (e.g. the file backend option for Glance, mounting an export to /var/lib/nova/instances on compute nodes), but for Cinder it will become a default in Icehouse and later should the OS resident on the compute node support it (and, of course, if you're using the NetApp NFS Cinder driver). The review for the change is here:
https://review.openstack.org/#/c/71279/
Once that gets accepted into Icehouse directly we'll evaluate providing a back port for Havana.