No idea. When they picked Matt Smith, they kept it fairly secret. I saw in an interview that Matt Smith was asked not to tell anyone until the episode with his first appearance aired.
While this isn't the interview I saw, it shows the process that was used for picking Matt Smith as the 11th Doctor: http://www.dailymail.co.uk/home/moslive/article-2195825/Doctor-Who-How-Matt-Smith-Karen-Gillan-discovered-breaking-hard-do.html
I read an interview with Neil Gaiman saying that they intended to pick an unknown, much like what they did with Matt Smith. They said a well-known actor brings too much of their past roles with them and would rather have an actor known first and foremost as The Doctor.
I don't think it'll be John Hurt, my gut feeling is that he may feature in a spin-off focused on the time war between the Time Lords and the Daleks.
That's what I'm thinking too. My best guess is that he is the version of the Doctor who destroyed them and the time lords, and is burdened with that knowledge. After all, the time war has only ever been referenced and never actually shown in the current run of the show, and as far as I'm aware, never shown in the previous run of the show.