When you compare Cloud Run vCPU pricing with preemtible VMs it becomes nearly 13x the price.
Most use cases could trade startup delay for reduced costs by running GKE with preemtible nodes and Cloud Run on top of it. Otherwise "normal" Cloud Run and Cloud Run on GKE could be combined into a system where on the first request an instance on serverless Cloud Run is started and simultaneously an GKE Cloud Run instance of the same container is ramped up to take over.
Most use cases could trade startup delay for reduced costs by running GKE with preemtible nodes and Cloud Run on top of it. Otherwise "normal" Cloud Run and Cloud Run on GKE could be combined into a system where on the first request an instance on serverless Cloud Run is started and simultaneously an GKE Cloud Run instance of the same container is ramped up to take over.