I'd rather he didn't. I much rather the story focuses on being 11's final stand and allow for his fans to witness him go out in a bang (or a whimper, depending the story). The new Doctor will have his share of adventures, no need to rush.
Until the plot synopsis leaked, I thought the regeneration would come at either the Act 1 or Act 2 point so that the story would end on an uplifting note.
We know that Capaldi has at least a scene in "The Time of the Doctor" as Jenna Coleman has said that he has dialogue in the episode. Though it could be something as simple as, "Change, my dear, and not a moment too soon!"