At the moment I only have room for one more story, so I'm swinging for the fences! I'm hoping for a (long or short term) MFF story, either with two female writers or one writer playing two characters (I'm open to sharing 'control' of one of the females if this is overly challenging).
I've included some ideas below, and most can be used in long or short term plots. I'm very open to new ideas if anyone additional plots, genres, themes, anything. I'm up for non-con, romantic, whatever there's a desire for.
1) (supernatural master-slave) A demon and his succubus minion chance upon a mythical female humanoid creature with potent energies for him or both of them to feed on. The succubus is jealous of the attention the new victim is receiving from the demon, so she takes her frustrations out by making the experience rougher/more intense for the victim (who perhaps gets off on domineering the victim).
2) Similar to the one above, except the male is the potent creature, and two succubi compete or otherwise cooperate to steal his life energies.
3) (Modern) Once the bride is drunkenly asleep after her bachelorette party at her house/hotel, a male entertainer is left with two bridesmaids who are similarly intoxicated and thoroughly aroused by the night's events.
4) (Game of Thrones) Lord Littlefinger is just arriving in King's Landing as the new Master of Coin. He has bigger plans than just the realm's accountant though, he's setting the groundwork for a brothel! This story would show Baelish's first employee or two being hired (after a competency exam?), and the trials of running a high-class brothel in King's landing. Eventually, he will task his first employees to help him run things, and throughout the process there will be intrigue, questionable morals, and whatever else happens in a brothel.
(Non-con, any genre) A male and female crime duo take a female hostage. After learning there won't be any ransom for her, they consider what to do with her. The female criminal can either have a penchant for domineering other women, or both criminals could simply want to have their captive for their combined uses. (Master-slave/harem, fantasy or sci-fi) Two female slaves entertainers are won in a game of chance by the male character. Their new owner has a bit of a conscience not to use his new slaves sexually, but his morals slowly erode. An eye for making money, though, he slowly increased the eroticism of the pair's routine. He eventually decides to open a brothel empire, and tasks the two women with overseeing 'human relations'. (Harem) A teenage son of an emperor has had his first concubine for almost a year. While they enjoy each other immensely, tradition and custom dictates that he have another. The first consort immediately tries to establish authority in the bedroom, but the new addition is spirited and won't give up without a fight for his preference.
I'll add more as I think of them. Some of these lend more to scenes rather than long term stories, but who can tell until it's happening, right?
Let me know if you have any questions or suggestions!