Having finally seen the reveal of the new 13th Doctor, I will reserve my judgment on how well this particular regeneration is going to work until I've seen Jodie Whittacker's performance and her dynamic with her companion(s). Just because it's not something I personally felt the need for doesn't mean I might not end up enjoying it in the end (see also: Missy).
Also, given that the premise of the show is built around the Doctor getting a completely new and unexpected body with every regeneration, and that the concept of Time Lords regenerating as a different sex has been a canonical part of New Who ever since the offhand mention of the Corsair in "The Doctor's Wife" back in 2011 (a possibility which Moffat & Co. have underlined with increasing emphasis at least once a season ever since), I really don't have a lot of sympathy with the people complaining that the announcement came out of left field and violates the True Spirit of the show. The spirit of Original Who, maybe. New Who, which has already spent over ten years breaking almost every unwritten taboo of its predecessor, not so much.
In fact, as soon as Capaldi's departure was announced I felt pretty sure that the next Doctor was going to be either PoC or a woman -- but not both, because that would be an even more dramatic and controversial change, and therefore far too much of a risk for cautious TV executives worried about losing large segments of their traditional audience.*
But for those who are claiming that Steven Moffat only made this move due to pressure from more enlightened third parties and would never have thought of it on his own, I'd like to share a friendly reminder that in the 1999 Red Nose Day comedy skit Curse of Fatal Death
, which was written and aired six full years before the return of Doctor Who
to television in any serious form (let alone under his control), Moffat had the Doctor regenerate** into a blonde woman.***
Oh, and she was the 13th Doctor too.
*As it is, I will be quite interested to see the ratings for Jodie Whittacker's first few episodes as the Doctor. Whether they go up or down or stay much the same, I think it's safe to say that a significant number of the people watching will not be the same people who watched Capaldi and his predecessors. I've already seen one post from a former fan who considers the casting of a female Doctor as the last nail in the coffin of her (yes, her) waning interest in the show.
**After starting out as Rowan Atkinson and regenerating into Richard E. Grant, Jim Broadbent and Hugh Grant in rapid succession, and don't get me started on how much I loved Rowan Atkinson's Nine and how sad I am he wasn't canon because we'll be here all evening.
***Played in this case by Joanna Lumley.