Considering the amount of options to tweak the arcology's society I've always found it jarring how granular the population description is; slaves vs. citizens. I'd like to add some layers to that and allow more control over what the population looks like and have some consequences to such choices as well.
Citizens have now been broken up in lower, middle, upper and top class. The first 3 classes plus slaves create opportunities for each other; encouraging one of them will ripple through to the others. the top class only cares about how high the domestic product is, which depends on a the combined value of everyone living inside the arcology.
Slaves and the lower class compete for work. Because slaves are really cheap labor, though less efficient, they take priority. All jobs left over are available to the lower class. Note that also player owned MENIAL slaves do these jobs. The lower class will fall into slavery depending on the level of 'welfare' (mostly policy related) even during good times (and the player can snag them as usual), but when there are no jobs those without jobs will attempt to leave and many of those trying to get out will be enslaved instead (some going to the player). The amount of work available depends on a fixed amount plus the jobs higher classes need done and the prosperity value of the arcology. Additionally menial slaves will now die. Not a huge amount, unless your arcology is particularly cruel. This effects arcology wide slaves as well as player owned menials (fuckdolls and bioreactors not yet included).
The higher classes have more straight forward interactions; they do not get enslaved or depend on prosperity directly. Enslavement is confined to the lowest class because it stands to reason a higher class citizen is higher class (partly) because they are not fatally indebted. If they were, they'd be considered lower class. No need for further complication this way. There might be class mobility within the arcology; when there are enough high class opportunities fresh citizens could move in or middle class citizens move up. But it doesn't really matter who fills those spots as far as we are concerned.
Phase 1 of this extension is finished, the basic population interaction is in place. This seemed like the time to gather some feedback, before developing things further.
Phase 2 would be FS interactions.
Phase 3 would be policy interactions (potentially new policies and/or changes to existing ones)
After that we'll see what still needs work. Reworking rents, interactions with sector upgrades/specializations, compatibility with other areas of the game, etc.