I think in that case, you’d stick to whatever version of ChefDK had a version of Chef you wanted to use. In any case, we don’t have any plans to decouple ChefDK and chef-client.
I don't think the question is to decouple. I would just like to see a complete bill of materials of every chef-dk build. Which *exact* version of all the tools (chef-client, berkshelf, test-kitchen, ...) are in the chef-dk bundle so we can trace back which bugs are present in the different tools.