I don't think he's a future Doctor. I've read the theory that the John Hurt Doctor is the (actual) 9th Doctor...between Paul McGann and Christopher Eccleston. He's the one that fought in the Time War and ended it by wiping out both the Daleks and the Time Lords. That's why the Matt Smith Doctor told him that what he did (commit genocide) was not done in the name of the Doctor. It's just a theory but I think it makes sense. Also, the Matt Smith Doctor seemed to know him and how would he know him if he was a future version of himself?
Sounds solid to me!