This is perhaps a mix of suggestion and thought, but there have been discussions before on the physiology of Kerbals. Currently, Kerbals are modelled in a sort of "generic" cookie cutter manner. There's no "fat", "tall", or, as the focus of this question, "gendered" Kerbal to speak of. During the KerbalKon discussions last year, Tanuki-Chau asked the devs if there would ever be a "female" version of a Kerbal. If I remember correctly, it's something the devs sort of put off for consideration in the future, but that they thought it would be an interesting idea. Consider though, with no form of varied Kerbal currently present in the game: What if Kerbals were androgynous, like Gethenians from "The Left Hand of Darkness"? What effect on gameplay, or perhaps the lore of Kerbal Space Program could you see stemming from such an idea?