The Club of Rome’s reasoning may be based on how many of the ‘elite’ will be optimal for their maximum happiness. Then you just determine how many slaves are needed to support their lifestyle. That’s how these people think.
It’ll be interesting to learn how they will determine who will be the slaves and how they’ll corral them. My guess is they’ll make sure the group is from their own class/caste, but then convince them that their “knowledge” and “expertise” as “doers” will make them… “essential”…