At Coherence (withcoherence.com - I'm a cofounder) we generally agree that GKE and other managed k8s are best used for stateless workloads. Rather than move stateful workloads back, leveraging managed services will yield the best results in the long term. In the case of Redis on GCP, something like Memorystore is going to be a better fit than managing a nest of node pools over time (think about version upgrades, resources differences across environments, etc...) However, the complexity of managing the different kinds of configuration across GKE and managed services can be a nightmare.

That's a problem we're hoping to help solve, where you define your application and it's dependencies, and we help run it in the right way to leverage managed cloud services across environments without passing that headache on!