It's been eight years since we saw Robert Downey Jr. take the role of the big screen Sherlock Holmes and it had been so long we began to wonder if we would ever see the character again. We now know that we will, but it turns out we'll have to wait a bit longer than previously announced. While the third Sherlock Holmes movie had been set for a Christmas 2020 release, the feature has now been pushed back a full year to December 2021.
While release date shuffling is nothing new, it rarely happens without a reason, though the reason for this decision is not immediately clear. No other major releases have been announced to hit in December 2020 that might have sent Sherlock Holmes 3 looking for a more protected release window.
The film was already going to be going up against Avatar 2 in 2020 and will now instead be going up against Avatar 3. That's probably a slightly better position. The second film in the franchise, being the first one in years, is likely to draw a larger audience than the third, which will only be the first one in a year. It's like going up against Star Wars: The Last Jedi at the box office instead of The Force Awakens. It's possible the decision making was as simple as that.
Although, the more likely reason was simply one of scheduling. Perhaps production of Sherlock Holmes 3 needed to be pushed back and that resulted in the delay for the release as well. It could be that Robert Downey Jr. or Jude Law had something change in their schedules which has made the delay necessary. It could be that the script from Chris Brancato is taking longer than anticipated to finish. Perhaps another writer is coming in to rewrite or polish it which will result in it taking longer than previously scheduled.
It's also possible that the issue could be one of who is going to direct. Guy Ritchie directed both of the previous two Sherlock Holmes films but he has never been officially announced as directing Sherlock Holmes 3. If Ritchie is looking to direct, it could be his schedule that made the release date move if he won't be available to go into production later this year, Alternatively, it could be that the production is still looking for a director and thus had to push things back in order to have more time to find one.
In order to hit the 2020 release date Sherlock Holmes 3 would have needed to go into production later this year. Now, the film has an additional 12 months of breathing space. If fans have waited this long, they can wait another year.