There's been muttering that Matt Smith will be in the show in the future.
I wonder if he could be the 'other' Holmes brother mentioned in tonights show ?
I saw that Moffat said that Matt would be interested if it were the right role. (Which serves, I think, to disprove the fan theory that Matt left Doctor Who
because of a falling out with Moffat.)
He might make a good Stanley Hopkins, the best of the Scotland Yard inspectors and the one closest to Holmes in intellect. What if Sherlock had to work an investigation with someone who was just as good as him?
The other choice that would fit Matt -- and it's a very off-beat choice -- would be A.J. Raffles, the thief. No, Raffles doesn't appear in the Canon, but Raffles was created by Arthur Conan Doyle's brother-in-law (so there's a connection). Sherlock
Canonical anyway, so I don't see an issue with bringing in a character like Raffles from outside the Canon.