Honest question - why would you want stateful workloads in a separate cluster from stateless? Why not just use a namespace?
because namespaces aren’t a failure boundary.
If your api gets hosed, you can create a new cluster and tear down the old one and call it a day.
With a stateful cluster, you can’t do that. As such you put in a lot more care with eg k8s upgrades, or introducing new controllers or admissions/mutating webhooks.