July 16, 2017

First of all,

Now that I've got that out of the way, it was not just introduced to canon last season. It was implied in the regeneration scene that introduced Matt Smith. Time Lord gender changes became canon in the Season 6 episode, The Doctor's Wife, with the discussion about the Corsair. The female incarnation of the Master was introduced in Season 8, (last season was Season 9). Last season showed an actual on air gender changing Time Lord regeneration.

It has never in the history of Doctor Who been established canon that Time Lords can't change gender. It just wasn't established canon that they could, and even back then, the idea was seriously considered and often teased.

So, it was always going to happen sooner or later, and it's been canon since 2011, and implied earlier than that.

I'm just extremely grateful that both Moffat and Chibnall are more progressive in their vision than many of the dudebro fans.