I would love to see more dimorphism in the pokemon world, but it would also mean more time/work devoted to art assets and it is likely their team already has their hands full. Masuda himself said this game took more work then any prior game just on account of the designs/additions to the pokemon roster alone. Eventually, dimorphism for genders could be done, but then you're going to open a whole new can of worms where people are like "Ugh the girl looks dumb, blah blah" for a given species.