Have you considered using OpenShift instead of Kubernetes? It comes with vastly improved multitenancy features, as well as other aspects, in regards to plain Kubernetes. OKD, the open sourced package of OpenShift allows full self-hosting: https://www.okd.io
This is what I'm trying to convince my current company about. They want everything in a single cluster (prod, test, stage, qa).
Of course self hosting makes this more difficult to justify, since it is additional expenses for more machines.