I would love to see a dark fic that is cannon up to the point where Harry kills Voldemort. In the scenario Voldemort won and Harry is believed dead (Narcissa is dead too, I don't really like stories where Lucius cheats on her in any manner.) Hermione is captured by Lucius, who is not as horrible as she's believed, though still an elitist and quite the terrifying person when angered. I believe you can write him in character while giving him a softer side that she hasn't seen before. Lucius seems to have no interest in Hermione sexually, but if you want he can require sex of her as payment for keeping her safe. She finds out that he has a secret guest after a time and the secret guest, of course, is Snape who is gravely ill from his wounds at the hands of the Dark Lord, but still alive.
For whatever reason, Voldemort has gone completely off the deep end and is holding all the DE's children hostage. Lucius is desperate to save Draco and he enlists Hermione's aid to do this. Over the course of time, she starts to have feelings for Lucius, even while she is sleeping with and falling in love with Snape. She comes to find out that Lucius and Severus have been lovers for years, and this intrigues her.
The plot should consist of a great deal of sexual tension leading up to the moment when the three get together, and should also have more than a bit of intrigue an danger.
I hope this is what you were looking for. I would love to read it, but don't have the guts to do a threesome story yet myself.
If you do decide to write it, please email me at tambrathegreat@gmail.com, and I will gladly review.
tambrathegreat