Melody Pond, or River Song, was last seen as a mental projection uplink into Clara's mind giving the Doctor the confidence that Clara was indeed still alive and showing viewers that the Doctor always saw River, even in the times he seemed like he didn't. While River Song's story seemed to find a fitting end with The Name of the Doctor, her real life alter ago Alex Kingston has revealed she'd like to be a part of Doctor Who in the upcoming series. Since she is currently a part of the computer system in the biggest library in the universe, it would be feasible that the TARDIS could download her into its system and kill two birds with one stone by bringing back River Song and giving the TARDIS the voice that the Doctor has always wished it had. Since the TARDIS believes he is "Her Doctor" anyway, why not have the voice and image of his wife be the one to talk to him? Then they really would sound like an old married couple when they argue over what planet and time to adventure to next!