I would have announced a doctory male actor and a female actor so that everyone would assume she was the companion when the location photos started to leak and then do the switcheroo at Christmas and surprise everyone.
So much or the last series was ruined by premature reveals.
I also hope that Michelle Gomez is fibbing and we get a female Master and female Doctor face off a few times.
I will miss Capaldi though. He is a great actor and some of his episodes are the best the show has ever had and he is good in the not so good ones.