A theory I saw that I quite liked was that John Hurt is actually playing the Doctor from before the "1st" Doctor, that he did something that made him "hate" himself, and change his name to The Doctor. I'm not sure if I like it more than the valeyard or the 8th Doctor theories though.
Also would like it if the John Hurt Doctor was what the 11th Doctor saw in his "hotel room" in The God Complex