The lift off happened on the December 1st 2014, with CoreOS announcing they are building a new Container Runtime, called Rocket. This caused quite a stir in the community that was keen at evangelising Docker, as The Container Runtime. Now they(docker evangelists) have to battle with benefits that the other(Rocket) brings to the table. This news got even more significance because CoreOS was thought as the mother ship for the docker containers, and now it was launching Rocket.
But what CoreOS did, was not just launch Rocket but also launch a specification, that Rocket is an implementation of. Now, this specification as it is turns out is an Open Standard for developing Container Runtimes, with a lot of emphasis on the Security of these runtimes. This specification essentially captures the divergence of Docker from being just a Container Runtime, to a more massive platform.
Now its just over two months since that blast off, and the ground control seems to be stirring the ship quite well. Its always good to have this competition, this make the ecosystem more level grounded.