This is kinda minor, but I'd love to see different body types for slaves. Thin, average, athletic, muscular, chubby, muscle-chub... I know this is a very anime inspired game where really only one body type exists, but I feel it could add nice bit of detail to slaves to make the randomly generated ones more interesting. And you can always make it an optional thing, being able to disable body types if preferred.
It's small, but it's a nice detail, makes randomly generated characters more alive... and could attract more people... I know plenty of guys and ladies who like chubby guys myself, for instance.
Other than that...
Maybe capture bears and wolves and such for more bestiality options?