[GeronL]

He was introduced as a Doctor who abandoned his role as a time lord, since Matt Smith recognized him I don’t see he is a future Doctor.

[Tanniker Smith]

It's been pointed out to me that if you look at the clothes that John Hurt is wearing, he is dressed similarly to Doctors 8 and 9, which means he could have something to do with the Time War. He is either an older 8th Doctor or a partway regeneration (or some gobbley-gook to be spoken later).

Maybe that's the Doctor's secret. They're acknowleging the American-made TV movie! 8-P