Moffat talks the last few episodes of this series
on the BBC's website, closing with this about "The Name of the Doctor":
The episode is called The Name of the Doctor and involves our hero in a conflict that is very, very personal to him. Usually he’s saving other people, but this time he might be the one who needs to be saved. We’ll also find out what makes his new companion so impossible and there’s a surprise that no one has got right so far, and one that will change the course of Who forever!
That tracks with the rumored plot synopsis.
The personal aspect? His dead TARDIS.
Needing to be saved? Clara jumping into an infinity of timestreams.
Why Clara's impossible? She's been splintered through time.
Surprise that will change Who
history? There's a forgotten Doctor.