So starting with the Festival of the Lost update, there is an additional unknown slot in the Forsaken section of exotic heavies. One of those unknowns is 1k voices (if you don't have Acrius, there will be three unknown slots). Also, the Red War exotics and Forsaken exotics don't have an extra unknown slot further meaning the new one cant be acrius or 1k voices. After that leaker that said thunderlord in Festival, and now a new unknown heavy, i'm inclined to say he's right. (he did accurately leak an amount of forsaken info prior to the reveal.) Also, the game has the hud icon for Thunderlord from d1, found in datamines. I've seen a lot of speculation that it will come from the Master Ives quest on the 30th. It would make sense, getting an exotic from a quest about a cryptarch.