It depends on how you look at it. The Docker Remote API provides an abstraction on the OS substrate and definitely binds you a lot more to Docker and their mode

It depends on how you look at it. The Docker Remote API provides an abstraction on the OS substrate and definitely binds you a lot more to Docker and their model. The "rocket doesn't implement an API" means all that it isn't really doing much more than kicking off the container and using the existing OS substrate to manage everything else. I can see where for SmartOS & Windows the Docker approach is more flexible. If someone has already settled on Linux, but they have their own ideas about how to manage containers within Linux that have nothing to do with CoreOS, the Rocket model is going to leave them much more flexibility.