There are already aliens that don't have a gender like humans do. Even if they just mention it in passing, it doesn't really make a difference. If they are pushed into the story, it makes episodes featuring them awkward. Gay charcters always devolve into how gay they are no matter what, and then gay people get mad when they die. It will be the same here, except it will be harder to write about how not "binary" or how trans a character is.