There is one thing that my brain keeps coming back to: Trenzalore.
It's claimed that the Doctor must never go there because his grave is there. We theorize that this is the reason the Silence were trying to kill him.
But here's my question. How did the Doctor's grave get there in the first place? What event brings Future Doctor to Trenzalore again?
They land in a graveyard full of war veterans, long dead from what seems to be a devastating battle. We have effectively seen the Doctor's death -- his real
This isn't Lake Silencio where he can trick his death away. We saw his wibbly-wobbly timey-whimey corpse. I am really intrigued if this is something that will further be explored or contradicted down the road.