Re: 800th Episode - 2014 Christmas Special (Rumour's/Poss. Spoilers)
I'd dig the above structure. Would remind me of Old Who trilogies like the New Begginings Trilogy, where the Master came back, the Doctor regenerated, and the Master was defeated. In this case, the Doctor is confronted by his past, he will face his most regretful part of his past, and probably will deal with his unresolved enemies before regenerating.
"Spock...?" Kirk said, whispering.
"I am... most pleased to see again, Captain" Spock formally replied.
McCoy shook his head in disgust. "Oh, for crying out loud, Spock. Its been eighty years!"
"Seventy eight point four years, Doctor."
The Holy Three meet again, in The Return