Based on the hints so far, Octavarium still can't be ruled out for the encore. But I still think it will be ACOS.
I'm still curious about James saying there will be "some songs" (plural) that have never been played before. We know one of them will be TBP/STR, but I wonder what the other one or two could be. A B-side? Now that they've played SDV, and we know there's nothing from BC&SL (so it can't be TBOT), I can't figure out what that might be. Other than maybe they are referring to ACOS, which to my knowledge hasn't been played in full, start to finish. But I could be wrong about that.