My Sherlock prediction
Just to get this up before it airs.
I don’t have a full-blown theory for how Sherlock faked his own death, but I do have an idea about the one obvious clue that everyone missed that Moffat mentioned a few times.
The preceding episode. The Hound of the Baskervilles one. There’s a chemical there that makes people hallucinate their own worst fears. When Watson sees Holmes fall off the roof, his worst fear would be that Holmes is dead. So when he checks the body, that’s what he sees.
I won’t speculate on the rest of it, but I’m almost convinced that will factor in somewhere.