Rancher 2.0 was my first time actually having a working kubernetes cluster, and I was initially perplexed as to why helm charts couldn’t claim storage. I installed Rook with the default example cluster yaml files, tweaked very slightly, and had working PVC for helm charts no issue. It seems like you could find a way to provision a rook cluster with the rest of the k8s infrastructure pretty easily. The replicated, always available storage is something that would really add some oomph to Rancher
I also like rook for the replication, fault tolerance that ceph offer plus the nice dev interface they provide: object store compatible with S3, FS or block store.
Rook is now part of CNCF so it may be great to support it at some points https://www.cncf.io/blog/2018/01/29/cncf-host-rook-project-cloud-native-storage-capabilities/