I think this game changing finale which changes the whole show bla bla bla is simple and been staring us in the face since episode 1 of series 7. So here it is...

The Doctor will lose his memory and forget who he is, this is why we have Clara's popping up randomly telling the doctor to remember, maybe he's running away from something. It also explains why we were introduced to "memory worms" in the snowman. To add to this, it would explain the 50th anniversary, Eleven won't have a clue who he is so wont remember the situation when he was Ten. It would completely re image the show, maybe series 8 can then be focused on him getting his memories back.

I can just imagine The Doctor getting memory wiped and him asking who he is to Clara, when she replies The Doctor he asks the question that changes everything... "Doctor Who?"

Interesting theory.
we'll find out in 2 weeks whether you or anyone else theories are right

But wouldn't he remember the situation as Ten BEFORE he loses his memory?

So right now he should remember experiencing it and be prepared to lose his memory.

I'm sure this could be explained some how