I'm working on a project that allows you to put a special "yaml shebang" at the top of any kubernetes manifest. The shebang is actually valid yaml since it's interpreted as a comment. This allows you to combine the declarative kubernetes spec (yaml) with external controller (kubectl)

example my-app.yaml

  #!/usr/local/bin/kubectl -f
  ---
  apiVersion: v1
  kind: Namespace
  metadata:
    name: my-namespace
  ---
  apiVersion: v1
  kind: Pod
  metadata:
    name: my-pod
    namespace: my-namespace
  spec:
    containers:
    - name: nginx
      image: docker.io/nginx:latest
      ports:
      - containerPort: 80

after making my-app.yaml executable you can now invoke the application's config to reconcile itself

  > chmod +x ./my-app.yaml
  
  > ./my-app.yaml apply 
  namespace/my-namespace created
  pod/my-pod created
  
  > ./my-app.yaml get  
  NAME                     STATUS   AGE
  namespace/my-namespace   Active   8s
  
  NAME         READY   STATUS    RESTARTS   AGE
  pod/my-pod   1/1     Running   0          7s
  
  > ./my-app.yaml delete
  namespace "my-namespace" deleted
  pod "my-pod" deleted

obviously this is just a simple example but there is come really cool potential here.