With docker swarm it's taken them this long to get simple secrets integrated, and as with all of my experiences with first party docker tools: they seem ok at first, but the devil (and problems) are in the details.
I trust Google more to get this right, and I highly doubt Kubernetes is going anywhere.
Kubernetes is also based on years of running containers with Google itself, it solves real problems. Allowing containers to run in the same pod allows for much nicer composability than running multiprocess containers.
Have you tried setting up a k8s cluster recently, I believe they added kubeadm for much easier setup in 1.5, which was released a few weeks ago.
Why are you equating low barrier of entry with quality? I think MongoDB ought to have taught everybody in this field that you can have a low barrier of entry and still be a crap product.
Kubernetes whilst a cool product still has a lot of rough edges even now. One I encountered recently was that to upgrade a locally deployed cluster from 1.4 to 1.5 the answer appears to be "re-install from scratch" as the upgrade script is still "experimental" (https://kubernetes.io/docs/admin/cluster-management/#upgradi...)
Add to the fact that Docker Swarm is adding Enterprise features (such as Secrets in 1.13) and that is has an Enterprisey version (Docker Datacenter) which supports multiple teams, why would I - an Enterprise developer and architect - look at Kubernetes over Docker Swarm?