the OP clealy pointed out that this was a suggestion for civs that dont find this unacceptable.
Toady isn't likely to prioritize modded civs over other features.
Its worth mentioning that with openly accessible conquering interactions, the slave to civilian raid function for the ethic is mundanely going to be ignored or goblin populations will quickly assimilate conquered provinces under a mass of troops as they usually do in a extremely fast manner.
Hence the original set of ideas offer subset, which you may argue is more of a modified scenario type fortress, forcing upon a deviancy in possible changes to architecture, jobs and town planning (razed and built buildings) for the settlement's new purpose as a slave camp. Passively in worldgen-activegen the proposed slave camp settlements offer a incentivised munciple benefit to goblins without exaggerating their population activated by their successful military campaigns versus other civs.
In much the same manner you may think that [ITEM_THEIF] civilisations may be able to stealthily hide themselves inside razed or abandoned sites alluding to the buggy behaviour that already happens when kobolds in catacombs survive wars/site population destruction because they are stealthed non-participants and take over the site by accident. Which now reflecting upon it isn't that bad a idea.
- Concealed item theives & bandits can claim settlements as a map visible forward base of operations and increase their native numbers in the area, bandits would become a implicit non-interfacable civilization like necromancers crossed with the skulking sieges of Kobolds when this condition and threshold is reached, and regularly demand tribute from local areas.