Back several years ago I went through an extreme sci-fi reading binge. I read Ian Banks Culture series and Peter Hamilton's Commonwealth, and Nights Dawn. I know sex changes were mentioned in the culture series, can't remember if they were mentioned in Commonwealth.
So the massively advanced humans of the "The Culture" could change sex at will. The process took several weeks if I remember correctly and the old anatomy would be absorbed into the body while new anatomy developed. Changing one's sex and gender every now and again was considered a normal thing to do. It was abnormal not to live for a time as the opposite sex.
I also remember reading "The Forever War" in which in the future humanity develops heterophobia as the entire population turns homosexual, then eventually becomes a single person.
I read the "Left Hand of Darkness," not to long ago.
I imagine if we don't face another dark age, if we don't wipe our selves out, eventually humanities attitude will change, think how much it's changed in the last 50 years.
Any other interesting sci-fi reading anyone can think of?