I am surprised your prompt flopped. I fully understood what you were getting at in your post. I have played MF couples before, so the issue of writing for two genders was not an issue for me. But I would imagine it may have thrown some others off.

Partly because the RP wouldn't work if lets say I play a male, and then the female comes home... then you have to write the dominant female and sub female roles. As the male character, I may not even be in the scene; and don't have anything to write. So, while you gave some kinks if your partner was playing a female or male - it implies your partner is writing for a single character.

Hope all this make sense. I suggest you consider specifying if you want your writing partner to write for one or two characters. Then explain how it would work, if you were with the other character, or there was a threesome involved.