This is a good idea for several reasons.
1) The Doctor Who series has received a lot of flack for never casting anyone other than a white dude for the role, despite the fact that as a Time Lord, the Doctor can regenerate into theoretically any body.
2) Hayley Atwell is an excellent actress with noted nerd cred, starring as the titular Agent Carter in the Marvel TV series. Frankly, the personality of Peggy Carter—smart, tough, feminine, awesome—could be transposed as the Twelfth incarnation of the Doctor almost wholesale.
3) Having announced that she wants to be the Doctor, I will hunt down and destroy all those who stand in the way of this brilliant self-casting. I will take no joy in it, but I will do it, because this is just too perfect not to happen. Our lives mean nothing compared to the possibility of seeing Hayley Atwell walk out of the TARDIS with Agent Carter’s look of steely determination on her face.
- Rob Bricken of i09