Red Hat's Vincent Batts gives a presentation at systemd.conf 2016 conference entitled, "What's next for containers?". It is a good overview of where the various container projects are (with no mention of OpenVZ however) and what work needs to be done. I enjoyed his assessment that the first thing that is next is, "Get Past the Hype," and to, "Make Containers Boring." Vincent goes over several of the userland tools as well as covers the areas where Linux native containers still need work. Enjoy.