Anyway, it still keeps preying on my mind that Sherlock can not deduce that Moriarty is dead from TAB. It's his crappest deduction ever. We're not even shown flashbacks to back up the idea that Moriarty was truly dead (the empty back of his head exists only in Sherlock's mind palace, for instance). And we are given the extra information that the body was never recovered - what? Why not? He could deduce from TAB that it was possible to fake a death, with help, and in fact TAB more or less shows what he did in TRF (fake the moment of death, then use a real body).
So why does he say that knows Moriarty is dead, and what he's going to do next? Is that just for the audience (Moftiss really wanted that mind palace Victorian episode, but had to have a deduction at the end). Or is it for Mary's benefit (he knows that she knows something)? It's Mary that he tells that Moriarty is dead. Has she taken over from Moriarty? Or does she know Moriarty's alive, and Sherlock's trying to pretend he hasn't guessed? Is she Moriarty's twin (she's not English)?
But he looks away from her when he says he knows exactly what he's going to do next. I think he might looking in Mycroft's direction, but I'm not sure - he doesn't seem to be looking at Mary or John. If it's Mycroft, well, I keep coming back to that filmed handshake between Mycroft and Moriarty - of course they're going to double bluff us and use it in S4! Is Moriarty the other one? Is he Sherlock's twin? (Yes, I know, but I keep coming back to "it's never twins", too!). Is he Sherrinford?
I don't know if those are dark enough .... what would be really dark would be John going evil and calculating, but then it wouldn't be John, and I think we need John as he is.