So three suggestions and I've no idea if they're new or not, but I'm really enjoying the game and ideas are just springing up. Firstly, it's a little silly for a 10ft cow girl to fuck a 2.5ft imp with a 3ft penis and for the game to treat that as normal sex. When the size diff becomes large enough, how about a subset of "treat like an onahole" positions?
And secondly, I don't know if this should be hard to implement, I don't feel like it should be, but how about a new slave job where instead of assigning them to your bedroom, you assign them to guest bedrooms. Could be free, could be paid for by the guest, leading to a little income. Not gonna lie, the possibilities here are twisted and great.
Third idea, how about tracking all of your direct bloodline descended from you? Even the ones you didn't personally father/birth.