Nothing, since no one has used that backend in years. Note that the LXC command-line utility is not the same thing as Linux containers, which Docker still uses.
It's not deprecated anymore. It's been removed. People have been using the native driver (libcontainer) for 2 years. LXC was deprecated in 1.8 and the code was completely removed in 1.10.
Well ... it's an alternate backend which has been known to be "a bad idea to use" since 0.11. LXC stopped being the default a long time ago, and anybody using it right now REALLY shouldn't be.
Not to mention that I'm not really sure that Docker Inc has strong feelings about semantic versioning (I don't work for Docker).
