You raise good questions Steve, a couple of points of clarification should help.   First, let's clarify what are "SQL Server containers?"   SQL Server containers are simply SQL Server instances created and managed with Docker commands and APIs.   They have a few added features specific to being a "container," such as a higher level of process and user isolation, and resource governance via the Docker API, and a private file system.   On the other hand they are normal full featured SQL Server instance that operates on the Windows host, and interoperate with all normal SQL Server tools.   Databases can be attached on the local host, or on network or SAN attached storage, and data persistence is no different than other SQL Server instances.   Containers add a private file system, which is a new option and provides a simple non-persistent option for working with data that is suited for dev/QA use.  But, there is nothing otherwise to distinguish Windocks SQL Server containers from other SQL Server instances installed on the host.   You have the same registry settings, the same features and functions, the same performance.  Containres work with all normal SQL Server tools, and are comprised of the same sqlserver.exe and DLL's.   

With Windocks SQL Server containers you get the best of both worlds . . . fast instance creation and great support for dev/QA use, as well as a complete, full featured SQL Server environment.   SQL Server containers support VSS and existing backup systems too.

Do "containers" add value in production environments?   While a container instance can be managed and patched just as any instance, the container "adds value" in production only to the extent that containers are a common infrastructure in a Continuous Integration and Delivery strategy.. In time I believe there will be interest in use of containers for production for "continuous delivery" and rollback strategies, as DevOps and CI processes are adopted.    But, today, the particular value of containers is realized in improved support of Dev and QA teams.

I hope this helps . . . I think this is a great discussion.