Interesting, because my rewatch had me swinging back towards the future incarnation. The lines that struck me came from the Great Intelligence:

GI: Welcome to the final resting place of the cruel tyrant; of the slaughterer of the ten billion; of the vessel of the final darkness. Welcome to the tomb of the Doctor!
[Later]
GI: It was a minor skirmish by the Doctor's blood-soaked standards, not exactly the Time War, but enough to finish him. In the end, it was too much for the old man.
Jenny: Blood-soaked?
Vastra: The Doctor has been many things, but never blood-soaked.
GI: Tell that to the leader of the Sycorax, or Solomon the trader, or the Cybermen, or the Daleks. The Doctor lives his life in darker hues, day upon day, and he will have other names before the end: Storm, the Beast, the Valeyard.
V: Even if any of this was true, which I take the liberty of doubting, how did you come by this information?
GI: I am information.

The Doctor thinks it isn't the secret that's been discovered, it's his grave; but it could be both. Perhaps learning one brought the Great Intelligence to the other.

And when we see John Hurt at the end, he's an old man standing among the graves of Trenzalore. Not that it means they're back on the planet's surface, in a literal sense; they're still inside the Doctor's time-stream. But Clara witnessed the various Doctors in many other settings within the time-stream, so that suggests this is a setting associated with the Hurt incarnation. And though the present Doctor seems to know about him, this may be because he's inside his own time-stream and can see the future.

I don't think it's conclusive, but I wouldn't dismiss the future option yet.