Smith: I could be a curator. I'ld be great at curating. I'ld be... The Great Curator. Ha ha, I could retire and do that. I could retire and be the curator of this place.
Baker: You know, I really think you might.
Smith, staring in astonishment: I never forget a face.
Baker: I know you don't. And in years to come you might find yourself revisiting a few, but just the old favorites.
Read what you will into those lines, I took it to mean a future reincarnation of The Doctor, beyond the 13th. A Doctor who's retired and taken up curating.