Re: The Curator.... Who is he? (SPOILERS for "The Day of the Doctor")
If Tom Baker had proved unavailable, I think David Bradley would've been a good choice... He'd have supped for Hartnell, as per the Adventures in Space and Time.
If anything, it'd been a nice nod back to that's ending.
"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