3. Time Lords Can Change Gender/Race
Whether the Doctor could be a woman has been a subject of fervent fan speculation since Tom Baker suggested that his replacement could be female. However, it wasn't confirmed in-show until the new series. Such a regeneration was first hinted at during the Eleventh Doctor's post-regeneration ramblings, and then in a line of dialogue about the Corsair in Series 6's The Doctor's Wife. Then, in Series 8, it was all confirmed, as Missy, a female version of the Master, appeared. Likewise, a regeneration that caused a change in race has long been a subject of speculation, especially since all incarnations of the Doctor have been white men. However, a cross-racial regeneration has been shown in the new series when Mels regenerated into River, suggesting that Time Lords can change race as well as gender when they change their bodies. While these changes have been controversial, they do allow for Time Lords and even the Doctor to be played by a wider range of actors. This is probably a good thing for fans, as it'll allow for a greater variety of interpretations of the character with the role open to more people, which will be a joy to watch unfold on screen.