To be honest, I don't have any specific ideas in mind! I've been having trouble finding people interested in a Repo line. I guess the most obvious would be a pre-movie line that explores their early relationship, through marriage, pregnancy, etc. I love AU lines, too. It might be a bit out there, but maybe a line where Marni didn't die - like, Nathan was led to believe she died, but Rotti's doctors were able to save her, give her blood, new organs, whatever. BUT, perhaps she was in a coma, and he kept her hidden, wanting to punish Nathan. Nathan would still lead the same life as a Repo Man, poisoning Shi's blood, etc. What would happen when Marni suddenly woke up to discover the monster her husband had become?
I'm just throwing ideas out there as they come to me, so I'm not married to any of them, and I'd love to hear your input, as well! Or, if you have some ideas of your own, I welcome them.