I don't see much use for the caste system with our current cities, they don't have a large enough food supply to support specialists. I would say that we should change one of our civics to take advantage of the single turn of anarchy we'll have for switching two civics at once.
Looking at the next city we'll found I see there may be an opportunity to create a GP farm, which caste system would aide in, if we decide on a GP farm city location, I would support caste system, otherwise slavery has less upkeep, and would be more useful with our food starved cities.