This is where crazy VM engineering can come into play. Something like a "Triple-passive" 3-VM server - it hosts 3 VMs, each is the passive node of a 2-node SQL

This is where crazy VM engineering can come into play. Something like a "Triple-passive" 3-VM server - it hosts 3 VMs, each is the passive node of a 2-node SQL Cluster. You start with 4 identical servers, running bare metal on 3 and a hypervisor on the 4th. In normal operation, the 3 bare metal servers do all of the work. But when one goes down, the role moves to the VM, where it might run in degraded mode until the physical server is restored.