There are already so many Dockerfiles out there and guides based on them. Plus you get filesystem layering, the cgroups, process limits ... I have a feeling it

There are already so many Dockerfiles out there and guides based on them. Plus you get filesystem layering, the cgroups, process limits ... I have a feeling it would be possible to build a container system that's Docker API compatible, but uses zfs and jails under the surface. I think that's what the old "unmaintained" port did a few years back.