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.
Linux Weekly News had a write-up in their Weekly Edition last week... of Lennart Poettering's talk (Containers with systemd) at LinuxCon Japan 2015. That article should be available freely later this week... but I found a recording of what appears to be the same talk at a different event from April 2015. Here are the slides. Enjoy!
For those with iFrame issues, here's the direct link:
Here's some documentation on that stuff if you are looking for it.