Sherlock fandom has produced some very interesting what-if-John-and-Sherlock-were-born-the-opposite-sex fic.
Three versions of Sherlock and John as women:
In Arduis Fidelis by
mad_maudlin "A Study in Pink," as seen through the eyes of Jane Watson. Sherlock is still fascinating, but this characterisation of Watson is utterly compelling. (Genfic.)
Categories by
parachute_silks The beauty of this fic lies in its slow, careful pacing. Sherlock and Joan, and the way their feelings for each other are not so easily defined. (F/F, explicit)
Experimentation by
tristesses Male or female, Sherlock would be the sort of roommate to barge in at the most inconvenient moments. Which has interesting consequences for Joan. (F/F, explicit)