[PentiumBug]

IMO, theoretically, it can be done. In practice, the consensus seems to gravitate to no, do not do that.

My experience is limited to on premises deployments, but here it goes: it's way better to isolate with different clusters, not only for different clients or business units, but several per user (think, for instance, infrastructure upgrades).

I think that standing up clusters these days is better a much better proposition than just a year ago. For instance, at $WORK, we extensively use rke and we can set things up in minutes in a fairly automated way (Terraform & Ansible.)

Edit: forgot one bit: I know about namespaces, RBAC, network policies, etc. I still think, in this point in time, that multiple smaller dedicated clusters are better than one huge beast. Maybe the story will get better over time.