The Q was how does one manage large numbers of heterogeneous containers (VM sprawl was already considered a problem, but we said if containers took over the sprawl would be worse). At the time the primary container mechanism was Solaris Zones and people uses ZFS clone functionality to create per zone container file systems. However, this only really helps if your containers are homogeneous. I built a system that created container file systems out of composable layers. One would define template file systems as a collection of layers that are stored in local and remote layer repositories and these layers would be instantly unioned together on demand when one provisioned new containers. We also demonstrated that since heterogeneous containers are now easy to manage, we can not just use containers as lower overhead but similarly long lived VM replacements, but also enable them to be used ephemerally, opening up many new use cases.
You probably know of this by a different name today.