"In universe" they production has dropped seeds of the notion since "The Doctor's Wife" with the doctor switching pronouns when talking about a fellow Time Lord, the Corsair. Then, we had Missy appear, stating she was formerly known as the Master. Finally, in "Hell Bent", the Doctor shoots the lead General (not as attempted murder, merely as a delaying tactic). A senior looking white man collapses; we have the burst of regenerative energy and a youthful black woman stand to her feet, noting it was pleasant to be female...again.

Not only that, but Sidney Newman himself, the "creator" of Doctor Who, recommended that a woman be selected in the mid 80s, Alas, as he was no longer part of the production team, BBC programmer Michael Grade ignored his suggestion and Sylvester McCoy was eventually hired.

While admittedly there are those who object to this decision, quite loudly, the places I've dared visit have been overwhelmingly supportive of the choice.

Finally, as a straight male, I can lust after the Doctor without feeling awkward! ;-)

Sincerely,

Bill

Tempt the Hand of Fate and it'll give you the "finger"!