I noticed the same thing about FAQ, I had all those working in my kubernetes setup.
One problem I did have with Kubernetes was upgrading. In the 1.3 era, I used kube-up to spin up an AWS cluster. There was no upgrade path until 1.5 when Kops began supporting importing kube-up clusters. It almost worked automatically, but it somehow got the wrong setting for one of the subnet configurations. Once I fixed that though, it worked. I gotta admit I was pretty impressed.
The only other problem I can think of is security, everything inside Kubernetes currently defaults to having full API permissions. Obviously this is insane pants-on-head behavior.
In GKE I just use one cluster per permission domain, which is fine for one team (and 2-3 permission domains), but obviously for large orgs would be a massive headache.