I did a talk for PlatformCON about virtual Kubernetes clusters and the open source tool vcluster. vcluster allows you to create and manage virtual clusters, which are basically a control plane inside of a namespace on a shared host cluster.
In the talk I explain more about what virtual clusters are, why we need them, and some use cases. It's about 17 minutes so hopefully not too painful to get through :)
Have a watch and let me know if you have questions about vcluster.