CRIU has worked fine for a long time. I've used CRIU under LXC in a lab, and CRIU alone in production.

This problem arises because Docker positions their intrinsics as novel containers, even though there was an entire field of prior art long before Docker showed up. Hence your confusion and worry checkpointing will never be supported; it already was, but you didn't know about it, because to you Docker == containers. One of my many problems with Docker, because they feed that.

Look how easy it is: http://criu.org/LXC