I've tried out Pkl which is similar in spirit, and I think it's a real solution for k8s manifests. The only thing holding it back is industry adoption imo. It's leagues better than Helm, and mostly better than Kustomize.
See also: KCL, which is very similar and might _actually_ be "the winner". Time will tell.
I don't expect a winner personally, rather that there will be dozens of alternatives always. Like build systems, deployments are quite bespoke to organizations and legacy has a way of sticking around for a long time
Having used CUE, mainly outside of Kubernetes, I cannot see myself switching to KCL. I really like having a configuration language that isn't so tied to a specific system and which I can use with the Go SDK
See also: KCL, which is very similar and might _actually_ be "the winner". Time will tell.