The Wormhole wrote:
Based on the was it's been set up, I'm pretty sure John Hurt's Doctor would have been in the special regardless of if Eccleston showed up or not. Since he's not, it just means more to do for Tennant and Smith.
quotes the costume designer in an article
on the Prince of Wales' visit to the set today: "There was a gap between Paul McGann playing the Doctor and Christopher Eccleston, when we didn't see a regeneration, and John Hurt will fit into that gap. He is a past Doctor, not a future Doctor." Based on that, besides the set-up in "The Name of the Doctor" itself, it sounds like Hurt's Doctor was conceived of as a separate character rather than a replacement for another actor.