I have a few ideas, and I apologize if they have been suggested before, or if they've been implemented and I haven't noticed them, or if they are absurd:
1) One thing I've noticed is that much of the game relies on gangs grabbing territory and such, there's little you can do outside of Gang Management to influence the gangs. If there were items the player could acquire that would boost gang stats, for example. Another option is that the player could assign girls to 'entertain gangs' which could boost morale and make recruiting more members easier (at the expense of the girl having to endure particularly rough sex with a bunch of thugs).
2) I hate it when a girl I like dies. I think it would be neat if there was a necromancer's tower you could go to to re-incarnate a girl. He would require you to transfer several girls to his tower so he could perform the necessary ritual sacrifice. I imagine he'd ask for the lives of multiple girls to offer up for the revival of a single one, as well as lots of money. Some girls are more ideal for the ritual - girls that are related to the player, in love with the player, of particularly high level or whatever - and would reduce the amount of time and money it would cost the player. (I see it as a building to whom all dead girls are transferred automatically, and to whom girls can be transferred manually for the ritual.) It could be extremely expensive given that it is a total luxury.
3) Similarly to the necromancer, if there was an alchemist (in the vein of FMA) who could create for you new girls based on girls you offer up for him to transmute together. Their stats, traits, experience would be combined into a single person. A sort of Frankenstein woman.
4) I've played a few Sim Brothel games where they have a bulletin board where slave buyers request girls with certain traits. I think these features are kinda boring because they just give you money and are infinite and indistinguishable, but I think if there was some sort of story context, even randomly generated little story text that ties in to the traits a buyer wants. Some examples:
- [size=78%]"A wealthy merchant who purchased a title in the court is seeking a wife for his son. Because of his commoner heritage, he has had trouble securing a fiancee of high birth that would ensure noble offspring. He would like a girl who is a princess or noble who is a virgin."[/size]
- [/size][size=78%]"A peasant and his wife have been having difficulty conceiving a child. They would like to adopt a teenage girl who has [various stat requirements relating to farming and animal handling]."[/size]
- [/size][size=78%]"A group of atheists have decided to throw in the towel and start worshipping a god. Finding none of the pantheon on offer satisfactory, and not wanting to affiliate themselves with the religious organization they scorned for so many years, they are requesting a goddess or fallen goddess of their own to worship."[/size]
- [/size][size=78%]"A prominent and ageing religious matriarch wants to marry off her son so she can pass her title off to a female descendant, as is the custom of her sect. Unfortunately, her son is more interested in men. She would like either a newly-impregnated woman of [stat requirements] whom she can marry to her son and pass off as legitimately pregnant by him, or a girl of [whatever high anal stats] to try to 'cure' him of what she views as his affliction."[/size]
I could come up with these all day. And would if needed.
The rewards could be money or reputation for the player or some other things.
5) A school structure where you can educate your girls. There is a Teacher trait - perhaps those with that attribute could teach there as well, enhancing the education. Perhaps there could be a Student trait too (given that so many anime characters are schoolgirls), and you could recruit girls here who have that trait or are 18.
Well, those are some ideas. If you got this far, thanks for reading.