There was a time when a few military institutions and even corporations used the term "Sir" to refer to both male and female members of heirarchy. The reason was to level the playing field of those subordinate. At the time, the men of the service were entirely used to calling their leaders "Sir." In fact, they did so automatically, as indoctrinated in them during training. When they first allowed women to serve in the military, the term was carried with them as well, to ease the transition of those beneath and around them. It carried the weight of authority for them more than 'ma'am' did, which was important for the psychological acceptance of those working beneath.
I'm not aware of it being used such anymore, but there was a time when it was common. It was also meant to give the women of the service, who worked so hard for their positions of respect, a feeling of being equal to their male counterparts in said authority and respect.
It is a throwback to that time, when it was considered progressive and equal instead of awkward. Their goal, literally as you say, was to be "Gender-Blind." In the 60s and 70s, when progressive movements started in earnest for women in the military, forward leaning aspirations from places like hollywood and television promoted this ideal and idea for blindness through..you guessed it, Sci-Fi stories, fantasy stories, and the like. Sci-Fi has always been a platform for pushing new human rights' ideas and presenting complex human issues in ways that do not offend or alarm anyone.
I honestly think that using the "Sir" for everyone, even in the minds of those watching the new series, makes us truly think of a society that has put gender-bias behind them in the military a long time ago and never thought twice about it, hence never changing the "Sir" to "Ma'am," which is another manifestation of "I'm not quite comfortable with this and need to seperate male and female authority in my mind."
