I think the reason the hole persists is due to the lack of production-ready client libraries for these configuration languages (e.g. Nickel) in Turing-complete

I think the reason the hole persists is due to the lack of production-ready client libraries for these configuration languages (e.g. Nickel) in Turing-complete languages and popular tools (e.g. Go, Kubectl, IDEs like VSCode and Jetbrains). Everything needs to be wired together with shell scripts and task runners. IDEs that offer autocompletion, smart functionality, and other first-class support for Kubernetes, Helm, Terraform only at best offer support for generic CUE or Dhall or Nickel via their LSPs. I think if you could kubectl apply -f production.cue, momentum would start to shift.