Its gonna get timey-wimey people......the Bad Wolf involved in the Time War before she ended it for good in Parting of the Ways? The tenth and eleventh involving themselves in their own past...my head already aches!
An important point. Both the Anniversary story and the Christmas Special are going to be watched by an awful lot of the "not we". Will they make for good stand-alone adventures, or will the necessary back story / plot resolutions (some going back 4 years) simply alienate the casual viewer?