I dropped out of watching Doctor Who on Capaldi's last series, I could already tell it was getting to be a progressive propaganda show that I didn't want to support. This guy...I don't know. It feels weird to have an African actor play the Doctor. Not necessarily wrong, just weird. Part of a pattern of making characters and roles that are traditionally played by men of white European descent into not that because replacing white men is good I guess. It can work storywise because of the Time Lord regeneration and all that, but it's still part of the pattern. Anyways, not something that really affects me since I don't really watch Doctor Who anymore (does anyone?)
Time Lords regenerating into different ethnicities and of the opposite gender is a creative thing they introduced in the last decade or so, IIRC (unless it was mentioned in Big Finish's stuff over the last ten, twenty or so years). In-universe, it's always been possible.
The first mention was when the 11th Doctor mentioned that an old friend of his, the Corsair, was a "bad girl" when they regenerated as female: They always got the same tattoo though per regeneration, so that's how he recognized the severed arm in that episode with the Sapient House eating Time Lords and TARDIS' (the Doctor's Wife).
Since then it's been retconned that all Time Lords can do it (mentioned by Missy/the Master, seen when the General regenerated back into a Black chick from an old White dude, then the writers using it to take a shot at males by having the General say, "How can you men have that much ego" or something).
In reality? Pre-2014 (IIRC that was when The Doctor's Wife aired), Time Lords always regenerated into the same gender and same ethnicity; Hell, fucking Romana was swapping appearances like she was changing clothes (which is why she looked like Princess Astra -- in reality the same actress signing on because they liked her acting so much. I think there was something more to it as well like she was marrying or fucking one of the Doctors. I dunno).
The change was done because of a) the BBC. 'nuff said and b) pandering to the less than 3% of the population that's of the Kitchen Sink Community -- and much less of that 3% even watch the show.
So, yeah.