Maybe there could be an option on how hung your character is. If you want to play a sub playthrough, you could pick a small size and be more receptive, whereas if you want to be a dom it might help to not be the only person in the whole game who isn't packing. They could have perks attached to that as well.

This would be a cool game mechanic but I also think that they should maybe include  pictures/animation for you being dom as well