I’ve spent some hours taking a look at Docker containers and how they connect to the network. The short summary is “messy” and better description is “train wreck”.
Chris Swan has a 30 minute presentation on his experiences with Docker as part of his company VNS3.
At this point in time, Docker networking is good for single application uses but would certainly require an extensive overlay/control system to enable for multiple applications & multi-tenant uses. In some ways, the use cases appear similar to NFV/SDN and thats why Kubernetes et al are relevant.
Lots more to learn on this topic and Docker seems to have a lot of legs now that AWS is offering containers with very small billing increments.