So I've had two ideas that I've wanted to play for some time, and each one requires a different type of female lead.
My Son My Dom.
The first is an incest one about a son and his mother. The father died/left when he was young and thus required him to grow up fast. The two of them are very close, and often times would end up falling asleep in the same bed, though nothing sexual happens. Think up late watching TV, and falling asleep. The mother is the first to realize her attraction to her son.
The underlying theme is love and that the son wants to see his mother happy. The son at some point (details to be discussed /discovered later) becomes aware of his mothers kinks (toys, bdsm, etc) and wants to act them out with her. Which may require a bit of a learning process for him as well.
My Worst Fear, My Biggest Turn-on
A man who is worried about his wife cheating is consumed by the idea. It doesn't help matters that she confessed her biggest fantasy is to fuck two men at the same time. What started out as an idea that crept into his head while he was masterbating, coming home to find his wife fucking at least one other man, has become one of his biggest fantasies. He decides to tell his wife he'd like to explore opening their marriage up for her.
This can involve various degrees of cuckolding and humiliation. Though occasionally the wife will still fuck the husband.