Sorry if this has been discussed before, but it's something that keeps occuring to me. We see in The End of Time how angry Ten is that he has to die, actually getting pretty nasty about it at one point. Let's just assume for a moment that his personality lives on somehow (past DW fiction has, I believe, actually had this happening, with all of the Doctor's past regenerations being stored in a pocket dimension on dying). Could he not hate his situation enough that he might go mad, and seek to break free and prevent his situation from ever happening in the first place? I know it's only fanon, but I once read a rather interesting fan fic where Ten, upon dying, goes into a metaphysical room with all his past incarnations and they shun him because of his Time Lord Victorious thing, and being left on his own he begins to despise the Eleventh Doctor for usurping his place. So this is where I see a possible link to the Valeyard, who sought to destroy the Doctor and the Time Lords.