I see enough evidence in the dialog to support the opinion that the Curator is a later incarnation of the Doctor who has chosen to revisit an old, favorite face for a regeneration. It is equally possible, however, that this Curator is not the Doctor, but someone (maybe even a future companion?) with a quite playful sense of humor and irony who -like the Brigadier- came to know a few [future] incarnations of the Doctor quite well, and was thus able to learn all the information that he clearly has shared with Eleven in that scene. He clearly was involved in the acquisition of the Gallifreyan artworks. I hope we'll never know for sure. It is indeed a warm, sweet smile & wink to the fans-- and it should remain 'frozen in time' as the gem it is.