When you discuss CM being necessary, you are talking about using it on the host and not within the container.
Ultimately, operability and proper configuration inside the container is critical. Using a Dockerfile with no CM inside it is not much of an improvement on not using CM anywhere.
You don't need stateful CM inside the container. It's fine to fire and forget - use Puppet in apply mode or Chef solo. But there's a reason these tools are used in building AMIs and containers over scripting languages - we've come a long way over the past 10 years, and I still feel that switching to the Dockerfile as a configuration mechanism is like moving back to configure/make/make install.
What I'd like to see is a "script dump" output that still lets you create your yml configuration but converts it into shell scripts that you can call from your Dockerfile without any dependencies.
Of course, now you have an additional build step... and what could you use to tie everything together? make/make build :)