Real mode would not be an efficiency gain at all on modern CPUs. Even if they were not the case I think it would only have any use between containers and full

Real mode would not be an efficiency gain at all on modern CPUs. Even if they were not the case I think it would only have any use between containers and full VMs when you want more separation than the former but less weight than the latter, and there are various existing microVM options that seem to have a handle on that space.