After thinking about it a bit, I'd say the entire plot of the episode *could* be a Byzantium-esque allusion -- the whole ~this big important thing happened at Trenzalore!!! This is important enough to talk about it at length!!!~ and all the exposition about the Doctor having a good deal of knowledge of (and being markedly upset about) the circumstances of his death, and the GI taunting him about it, didn't really form a self-contained story and would be a tad pointless if it doesn't figure into later events.

However, having both this suggestion of the Doctor's future, and the evidence of the GI using only non-future examples you mention, figure in the episode could also just be Moffat's way of keeping viewers guessing about the placement and nature of Hurt!Doctor, making them more excited for the 50th because they want to know what's going on. The hints towards either one of the theories could be red herrings.