No, I'm not kidding. She has the chops to play aloof\weird\absent-minded, dark, etc.
The Doctor has mentioned before that he's not sure what he'll regenerate into. If it were handled with a nice balance of serious and light, it could really be interesting. They could go light on companions for a while too. Focus on the more solitary Doctor.
I'd dig a more edgy Doctor again, along the lines of Eccleston or the last several episodes of Tennant, particularly The Waters Of Mars.