Yes - I find docker and persistent volumes to still be a huge stumbling block. I have hit some troubles with Convoy NFS. But all that aside, no one wants to use NFS for production setups anyway anymore. It has caused me and my team enough sleepless nights.
If I had the resources, I’d rewrite every piece of code we have which expects some POSIX file system to store data to use a REST based object store instead (Ceph, or anything, really).
In absence of that, Flocker seems a nice solution to bridge this gap. A volume moves with the container. If a container has a flocker volume, you can stop it on hostA, and do a docker run on hostB, and it automagically mounts the same volume using whatever back end driver you specified (using vSphere for now, as this is all I have conveniently available in my lab setup).
I just still don’t know whether I can trust Flocker with my (paying) customer’s emails 
Feature request logged here for dynamic volumes:
https://github.com/rancher/rancher/issues/6303