Not OP, but a registry works anywhere, whereas a custom runtime doesn't (managed node groups in EKS, GKE, AKS etc). Additionally, once you use a custom runtime

Not OP, but a registry works anywhere, whereas a custom runtime doesn't (managed node groups in EKS, GKE, AKS etc). Additionally, once you use a custom runtime, now you have to deal with multiple runtimes in your cluster. You can no longer easily just run pods, you have to ensure they run on the nodes with the runtime for the images you want.