I'm happy to address any specific concerns you have about security. It's an important topic for me.
In this particular comment I could only spot one specific criticism: the lack of built-in user segmentation, so I will talk about that. I agree that this would be a nice feature. But we decided to not rush it, and instead tell operators to rely on the underlying system features for authentication, segmentation etc. In practice that means:
* If you have an https auth infrastructure in production, drop the appropriate middleware in front of your docker daemon, and rely on that.
* If you rely on ssh keys and unix access control in production, keep the default configuration of listening on a unix socket, and use regular unix users to decide who gets to talk to the socket.
* If you run trusted payloads, or if you run untrusted payloads with acceptable mitigation in place (no root inside the container, apparmor/selinux, inter-container networking disabled etc.), then go ahead and pool all your machines into a single swarm.
* If you run untrusted payloads, then map each trust domain to an isolated group of underlying machines. This is what Amazon, Google and others do when running customer payloads on Docker for example.
It would be a nice feature to segment Docker API endpoints by user, so that different users have different views (and different levels of access) of the same underlying daemon. But that requires implementing an authentication and authorization layer, and it requires changing some aspects of the Docker API which imply privileged access to the system. For example, the 'docker run -v /foo:/bar'. This represents serious engineering work, and as much as I would like to make you happy tomorrow, I don't think you will be any happier if we ship an unfinished feature.