Infinite riches (or more aptly no use of your hoard) for Morale and building is already a feature for Power Fantasy.
I don't believe they will ever allow for you to regain gifted prisoners except for a few key examples as it is can be a major pivotal relationship moment. (All 3 location Factions require a sacrifice.)
I meant more specifically a use of a unnamed female captive to sate the needs of your hoards (i.e. wolfmen kobolds and mercs). I get that it wouldn't make much sense for the storyline factions to do so, but in regards to the armies you recruit to keep morale maxed but now that I know it's a thing already, my question has been answered :) thanks