> But there is no equivalent system for whole clusters. To transition from one cluster to another, you have to handle everything that k8s gives you without relying on k8s for it

Ah, but there are. Maybe not a cluster orchestrator that would let you hot swap a single cluster, but if you're only running one cluster it's inherently a pet already.

One common way that I've personally used to solve this problem is use Federated Clusters (kubefed) to run multiple clusters with global load balancing so that even when one entire cluster goes away its traffic is just shifted to the other cluster (whether because of upgrades or unexpected outages of the control plane)