According to the April Online Meetup (linked in the following thread), this will be part of the HA Setup, which is coming soon, but not implemented as of beta3:
See: Rancher as container on its own host?:
"What Rancher technically is is an application that runs on Kubernetes as like Kubernetes controllers. Technically, the way it works is Rancher talks to Kubernetes and creates custom resources in Kubernetes and stores its state in Kubernetes. There’s two modes of how that works. If you do docker run, you’re running etcd inside that container and we’re actually running a fully embedded version of Kubernetes inside the one process… It’s all embedded inside of that one process, and it’s saving its state to /var/lib/rancher… so it’s saving its state to the local disk… So if you want to upgrade you can just do --volumes-from or bind mount /var/lib/rancher to some place on disk and that will save your state. So that’s one approach.
The other approach is you just deploy Rancher into a Kubernetes cluster… Rancher will recognize that it’s running inside of Kubernetes, and then it will use that Kubernetes cluster to persist its state. Its state will go into the cluster’s etcd… That’s actually how we’re doing HA deployments."