It's not like Docker is the ultimate tool. Docker, as far as I know, has very messed up networking, which is not apparent until you need anything non-standard.

It's not like Docker is the ultimate tool. Docker, as far as I know, has very messed up networking, which is not apparent until you need anything non-standard. Also, Docker is not as debuggable as a regular service started by initscript. It's not going to replace bare metal servers, virtualized servers, or even containers, on top of which it is built. Considering these, there will always be a place for configuration management tools, like CFEngine and its derivatives, or for orchestration tools, especially the ones that are not tied to a specific way of running things. I don't think Docker on its own can do much good in a heterogenic environment, and most of the big environments that lasted some time are heterogenic.