Recent years of Doctor Who have shown fans that Time Lords are more genderfluid than ever before, and certain hints in the show’s Season 10 finale point towards the possibility that the next Doctor might just be female.
At the start of “The Doctor Falls,” the Doctor is betrayed by Missy, who teams up with her former self, the Master, and reveals to the Doctor that Bill has been transformed into a Mondasian cyberman. Later, when everyone is more or less trapped on a higher floor of the massive ship, they’re preparing up for an impending cybermen invasion.
When a cyberman boards the ship’s elevator and approaches their floor, Cyber-Bill tells the three Time Lords to stand aside so she can defend them from the incoming robotic monstrosity. John Simm’s Master quips, “Is the future going to be all girl?” It’s the Doctor himself who says, “We can only hope.”
During Peter Capaldi’s tenure as the titular Doctor, Doctor Who has been more progressive in its representation of female Time Lords. In the finale, the Master’s comment about the future being “all girl” comes from his worry at having to regenerate into a woman. He also berates Missy and the Doctor for referring to Cyber-Bill as “her” when she’s been fully converted into a cyberman.
This follows up on a quiet moment in the previous episode in which the Doctor explain to Bill that Time Lords were “the most civilized civilization in the universe” and were “billions of years beyond [humans’] petty obsession with gender and its associated stereotypes.” In the Doctor’s foggy memory, he can’t quite remember what his or Missy’s gender were when they were children and he developed his “man crush” on them.
Missy’s prominent role over the past three seasons as a female version of the Master has been the most glaring example of a Time Lord’s potential to change genders, but Time Lords swapping genders with a regeneration has been canon for far longer.
In the Season 9 finale, “Hell Bent,” the Doctor killed the Time Lord known as the General while on Gallifrey. The General regenerated from an older white male into a black woman. Further back, in Season 6 episode “The Doctor’s Wife,” the 11th Doctor mentioned the Corsair, who was a tattooed Time Lord that spent several incarnations as female.
Barring any kind of official announcement from BBC, fans will have to wait until the December 25 Doctor Who 2017 Christmas Special.