Robert Downey Jr. still plans on making Sherlock Holmes 3, despite the project lingering in development for the past seven years. Shortly after starring in Jon Favreau's Iron Man in 2008, Downey Jr. continued his astounding Hollywood comeback story by appearing in Guy Ritchie's Sherlock Holmes in 2009, co-starring Jude Law as Dr. Watson. The film was based on a script by Michael Robert Johnson, Anthony Peckham, and Simon Kinberg, and it became an enormous commercial success, which is why Warner Bros. immediately commissioned a sequel.
Sherlock Holmes: A Game of Shadows hit theaters in December 2011, with Downey Jr. and Law reprising their roles as Sherlock Holmes and Dr. Watson, respectively, with Jared Harris joining the sequel as the iconic antagonist, Professor Moriarty. While A Game of Shadows wasn't as well-received by critics as the original film, it still earned quite a hefty sum at the box office to warrant another installment. Warner Bros. first revealed plans to develop Sherlock Holmes 3 in 2011, when they hired Iron Man 3's Drew Pearce to write the script. Unfortunately, after a series of delays, Sherlock Holmes 3 has yet to go into production - and the prospect of doing so seems less likely as time goes on. But, Downey Jr. is reassuring fans that he still plans on making the movie.
In an interview with EW for Avengers: Infinity War, Robert Downey Jr. casually mentioned that he still plans on making Sherlock Holmes 3 as well as several other projects. Here's what he said: "...We’re looking at another Sherlock Holmes, we’re developing Perry Mason for HBO. I still want to do Pinocchio."
Sherlock Holmes 3 was once expected to start filming sometime in 2016, but that didn't end up happening. Instead, the project got put on the backburner for Ritchie, Law, and Downey Jr. And the last time the film received an update was in October 2016, when Warner Bros. assembled a writers room for Sherlock Holmes 3, consisting of Nicole Perlman (Guardians of the Galaxy), Gary Whitta (Rogue One: A Star Wars Story), Justin Malen (Baywatch), Geneva Dworet-Robertson (Tomb Raider), and Kieran Fitzgerald (Snowden). The idea was for them to shape a story and a script for the third installment.
It's been well over a year since Warner Bros. brought together those writers, and each screenwriter has since moved onto other projects. For instance, Dworet-Robertson is now busy rewriting the script for Anna Boden and Ryan Fleck's Captain Marvel, in which Law also happens to be starring in a major role. Plus, Downey Jr. has been busy with Anthony and Joe Russo's Avengers: Infinity War and Avengers 4, not to mention Ritchie currently being tied up with Disney's live-action Aladdin film. But all that doesn't mean Sherlock Holmes 3 still can't happen sometime in the near future.
Downey Jr. wrapped production on Marvel's latest Avengers films earlier this year, and Ritchie is already in post-production on Aladdin. So, Sherlock Holmes 3 could theoretically go into production later this year once Law completes his stint on Captain Marvel (which officially starts filming this month in California). If that happens, then fans could be looking at Sherlock Holmes 3 hitting theaters within the next year or two, depending on when Warner Bros. would like to release the film. But we'll just have to wait and see what happens.