If there are future specials, I kinda want Moffat and Gatiss to revisit their original idea for "The Abominable Bride." Gatiss talked about it on PBS' Masterpiece Studio podcast, and the idea was that instead of going back to the 1890s they would do the 1940s, with Holmes and Watson fighting Nazis in black and white, instead.
Would Martin Freeman be playing Watson as an elderly dunderhead?
I've actually been thinking of trying to track down the Rathbone/Bruce movies, out of curiosity. I surely saw a number of them in my youth, but it's been ages.