It has been confirmed that Mr. Tennant will be performing with the RSC, next summer. He will be playing Hamlet--congratulations to him for that, and also will be doing a small part in another Shakespearean play, as well.
Alas, therefore this news is also confirming that Series 4 will be his last stint as the Docctor. (There's no way he can do both at once, unless the filming/broadcast schedule drastically changes--and somehow I don't foresee the BBC doing that).
He's not leaving yet, tho', and DT fans and Whovians alike, will have one more year to take in the wonderful performances of this highly talented and brilliant young actor, who has come to win the hearts of Whovians and non-Whovian's, all across the globe.
idiot... Doctor Who will take a hiatus. David will be back.