Actors like Ian McKellen, Patrick Stewart or Derek Jacobi might have played this character just fine. But I can't think of any other actor who seemed to have eccentricity and intensity so naturally built into himself as John Hurt, the perfect Sci-Fi/Fantasy actor. Neil Gaiman wanted him to play the Sandman.
Ian Mcshane might not fit the War Doctor but Anthony Hopkins might take a chance as the War Doctor have white hair and a white beard could be a great choice tho originally he was played by John Hurt with a Blackbeard one dont forget that hes called space Merlin and not Space Blackbeard.
Originally John Hurt was supposted to voice Starswirl the Bearded in Fim but Anthony Hopkins would be a second choice too sure i need to search who voiced Starswirl