I really like kubecfg--it's an unopinionated powerful tool that uses jsonnet to describe k8s resources. I really tried to make kustomize work but I found it really, really rigid.

I am, however, not sure what kubecfg's future is: ksonnet (its way more complicated cousin) is being deprecated.

Re: ksonnet deprecation: I heard from some of the CoreOS team at a Prometheus Meetup recently that ksonnet is not exactly being deprecated.

Heptio (the owners of ksonnet) were bought by VMWare and will no longer maintain it. But it's possible the CoreOS guys will take ownership since they use it heavily in some of their tools.