Characters like Sherlock Holmes or Harry Potter don't come along every day, even for their creators.
With this weekend bringing a second "Harry Potter" movie that doesn't include Harry himself, one starts to muse on a world where Sir Arthur Conan Doyle somehow followed the path of J. K. Rowling. It's well known that Doyle wanted to quit writing about Sherlock Holmes at at least one famous point in his career. But technology had not made it to the point where screenwriting was a valid career choice for a successful writer in Doyle's era, and given his attempts at breaking into playwriting, you know he's have been into screenwriting in a heartbeat.
And if movie adaptations had turned his popular literary character into a box office bonanza for Hollywood, combine that with wanting to get away from Sherlock and Doyle's love of history and you get . . . .
A Sherlock Holmes prequel.
Finding some way to put Brigadier Gerard into "the detective world of Sherlock Holmes," Doyle could have made Gerard his Newt Scamander. Or would it have been Professor George Edward Challenger who first appeared in a movie script from Doyle's pen, rather than a book? Or both? And more!
In any case, it's hard to imagine Doyle turning down a payday from simply putting a character he was going to write anyway into "the detective world of Sherlock Holmes." And suddenly Sherlockians would have new questions of "Canon" and "not-Canon" to consider.
A Conan Doyle shared universe is still something a clever writer might concoct, if one hasn't already. But the market to make it as big as Rowling's has long passed -- Sherlock is huge, but Doyle has suffered the fate of all writers, passing from "popular" to "classic." He can't surprise us with a new book or screenplay at this point, and that surprise is part of what makes marketing fall in love with a creator.
Still, it's fun to imagine what might have been in "the detective world of Sherlock Holmes."