I think Docker orchestration and coreos can coexist - if I had to use COREOS to use the goodness of Docker, then systemd-nspawn would come and eat Docker's lunch.
I wish that Docker bless one of Ansible/Chef as the official orchestration base and take it forward. I really don't want to earn something Docker specific.
Ansible/Chef orchestration IMHO solves a very different problem than container orchestration.
I agree that Chef and Ansible are different than container orchestration today - especially, when you look at low level stuff like networking, mounts, etc... But I guess what I was saying is that it is not hard to add these features to them.
They already have a specification format that works well and check for idempotency at its core. Unless you mean something like etcd is fundamental to container orchestration, which I don't believe it is (we run a couple of containers in production using Fig)