I think I have the same thoughts that the rest of my Flist does re yet another idea from another author co-opted by Moffat into an episode, in this case the Christmas Special. If he's not borrowing his own past ideas, he's borrowing someone else's, it seems =/
My husband thinks the episode's planning might have gone down a little like this:
BBC meeting to discuss a Doctor Who Christmas Special 2011.
Participants: Stephen Moffat and BBC television executives.
Moffat: "Alright, here's the pitch. There's a little girl. It's World
War II England...."
BBC exec 1: "Steven we're not remaking The Empty Child"
SM: "No no no, this is brand-new. It's a little girl. And she is
enchanted by The Doctor as something out of a fairy tale"
BBC exec 2: "Young Amelia Pond again?"
SM: "No no. There are monsters hidden in a wardrobe. And a lost and
frightened little boy."
BBC exec 3: "We're re-transmitting Night Terrors?"
SM: "BOLLOCKS! Let me start again..."
BBC exec 1: "Steven just one question. Is River in the script?"
SM: "No, why?"
BBC exec 2: "Alright, we're greenlighting it, let's just get it into
production and film the bloody thing, maybe we can stay under budget
this time."
BBC exec 3: "And hope ITV doesn't decide to put on a Downton Abbey
Christmas Special"