Such questions are answered — or at least teased — in a recent interview with Steven Moffat.
Not that Moffat is likely to give away any details of Season 4. “I can’t really say what we’re doing with that, but there is no last-minute whim in this,” Moffat says in a Vulture interview. “We’ve had what we’re going to do with Moriarty in place from before the second season. Exactly what we’re going to do.”
In fact the only changes to the Moriarty plan seem to have come in his first appearance on “Sherlock.” “Obviously Sherlock Holmes must have a Moriarty,” Moffat explains. “The thing that happened that was different because of Andrew was that, originally, in ‘The Great Game,’ the only scene that you saw Moriarty in was when he plays who we used to call Gay Jim. Gay Jim from IT. He comes in and Sherlock deduces that he’s gay. It was quite good.
“At the very end, Sherlock would have realized that he was Moriarty and that he’s just missed him. The great game has begun! But we weren’t going to see Moriarty again.”
When Scott auditioned, however, Moffat liked the actor’s rants as Moriarty so much that he used them to create the big pool scene in “A Scandal in Belgravia.” The villain thus became a bigger part of the series and his long-arc was set.
Audiences will just need to wait until Season 4 to find out more of what that is.