CoreOS only. They're on 4.8 right now and they update the kernel whenever is necessary to keep up with Docker needs. That's the only safe bet on the long term. (as stated in the Roadmap in the article).

Read: Even if Ubuntu 16-LTS and Centos/RHEL 7 may be up to date enough now (not sure), they won't keep up with the latest minor kernel updates and that will become a problem in 6 months when docker 1.1X will require THE newest kernel.

It'll be interesting to see how this plays out. RedHat is pretty invested in Docker right now via OpenShift so they have a lot incentive to backport required kernel fixes to Centos/RHEL 7 but at some point they'll likely have to drop support for the latest and greatest Docker release.

What makes you think they aren't just stabilizing/standardizing a single version of docker and backporting fixes?

After all, about 1/2 the gripes stemmed from the fact they docker itself is basically the engineering branch minus any serious regression/etc testing. Of course things are going to break from release to release, that is why test departments exist.

Ubuntu 16.04 LTS is on 4.4, and that package is available as a backport for 14.04: https://wiki.ubuntu.com/Kernel/LTSEnablementStack