You'd have thought that since the industry is nepotistic as fuck, and Cumberbatch is on the tail end of being everyone's j/o buddy (not to mention the whole WhoLock thing), they'd have cast him. Maybe if he'd been a woman they would have done.
At the age of five, Skagra decided emphatically that God did not exist. This revelation tends to make most people in the universe who have it react in one of two ways - with relief or with despair. Only Skagra responded to it by thinking, 'Wait a second. That means there's a situation vacant.'