I think D being androgynous would actually fit thematically and enrich his character.
D is in essence a "perfect middle". He's made to be a balance mix of polar opposites (Vampires-Human; Day-Night; Sacred-Profane, etc), and thus, its inevitable for him to be perceived as an "other" by both sides, leaving him without a real sense of belonging, staying in a gray area that no one really wants to claim and could be easily seen as an identity on its own.
Actually, the only thing we could say that he fits in is in the male role in society. And that isn't a full match either, mostly because his lack of interest in women or finding a partner in general. Seeing an already alienated guy being unable (or unwilling) to fit into such a construct as present in the work as gender roles and presentation, could further cement the idea of being an outcast for the rest of characters and would highlight the idea of D being "one of a kind".
The mere concept of D as a "success", has this dilemma as a direct consequence and it'd be interesting to see the narrative lean more into this ideas and take them to their bitter end. D can not fit because he's made for a new world that doesn't exist yet and is to be made with him as its core.











