Re: 800th Episode - 2014 Christmas Special (Rumour's/Poss. Spoilers)
Given that the Complete Series 7 box set will be released later October with all series 7 episodes and Christmas specials, I shall highly doubt that.
Plus, it wouldn't be the first time a series would begin and end with different Doctors. Think Series 4 of Old Who with Hartnell/Troughton, and accordingly Series 21 with Davison/Baker (on second thought, maybe you shouldn't
"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