Combom's picked up on a tweet by the Moff, [perhaps too obviously a red herring?];
An interesting tweet from Steven Moffat earlier this week;
Right EVERYBODY who follows me, go and follow @SophiaMyles - spin that fireplace. NOW. I'll explain later. Or not.
Of course @SophiaMyles is Sophia Myles who played Madame De Pompadour in the 10th Doctor story 'The Girl in the Fireplace', written by the Moff. Sophia apparently replied: 'Watch this (fire)place and also added 'The plot thickens...' [I'm not a twitter nit so have to take other people's word for all this!]
Will Moff play it safe, again, and go for an actress he's already used in Who? Maybe. Would he openly drop such a huge hint about the next companion? Probably not.
My feeling - maybe she will appear in the next series (or maybe Sherlock, which has been suggested elsewhere), but not as companion... she's two year's older than Matt Smith, which would, I think, be a bit odd...
My vote, if we had to recycle someone - bring back Michelle Ryan (Lady Christina de Souza), preferably in PVC catsuit! I mean, there's a loose end that needs tying up - last seen flying off in a red London bus... come on, surely the Moff can't resist the temptation to tie up every loose end ever in the history of the show... (now there's a challenge for him).