I've been telling my wife, ever since we watched the season closer, that John Hurt is an older version of the 8th Doctor...& it appears I was right.
During the royal visit, costume designer Howard Burden, seems to of confirmed it for me.
"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."
So John Hurt is the 8th Doctor after the Time War but before he regenerated into the 9th. Which makes more sense to me than any of the other theories out there, especially if you're like me and believe that the Doctor has been showing the signs of PTSD, after the Time War the 8th probably gave up being the Doctor and on life in general.
But that's just my theory. What do you think?