For me the sweet spot is monolith(-ish) 12-factor applications packaged up in containers. In this setup I can just `docker-compose up` my dependencies (postgres, redis, rabbitmq, other services, ...) and run the application from my IDE against those (so I can use the debugger instead of printf-to-cloudwatch). For production I can package the app in a container and deploy to a container orchestration platform (Kubernetes, ECS, or something else).
To answer your question, what comes after Kubernetes?: I'm hoping for a platform that is somehow a consolidation of the good ideas that we've seen in Terraform/Pulumi/Kubernetes/Cmake/DockerCompose/Swarm. I want to write a portable idempotent "deployment build script" that I can apply against a cloud provider or bare metal or localhost in a similar way. With good support for different configurations depending on the environment (like C ifdefs or cmake options).
For example: when I apply the script against my localhost it spins up a postgres container, when I apply the same script against my AWS account it configures an RDS postgres instance. Both invocations will pass along the connection string to dependant services.
Basically morph docker-compose.yml into a portable Cmake for container orchestration.