I was going to mention Triton/SDC. It does solve the security issues though it does it by running SmartOS. SDC is pretty cool but docker really needs to be secure in its own right.
It is also worth mentioning that since Joyent has implemented their own docker client, not all features are there yet. Last time I tried docker-compose didn't really work right yet. There is a full list of divergences on their github page. It has a lot of potential though.
Your larger point is correct, we're still working hard every day to add increase the support particularly for the newer docker apis and extensions. Now, docker-compose 1.2 is working in the production datacenters with docker-compose 1.3 in the east-3b (beta) dc.
I know that 'appeal to authority' is a bad argument technique but the Docker authors themselves have mentioned this repeatedly in the past. IIRC one of the holes was sysfs. Has something changed?
It's more that containers haven't been proven secure than that they are inherently insecure, so I disagree with the blanket statement "it's possible to break out of containers".
VMs have the advantage of shielding the kernel with a hypervisor, but they also have the disadvantage of lots of complicated driver code that can allow exploits such as VENOM.
It is also worth mentioning that since Joyent has implemented their own docker client, not all features are there yet. Last time I tried docker-compose didn't really work right yet. There is a full list of divergences on their github page. It has a lot of potential though.