For Silver, in comparison to it's other films of recent years, it was. From a Joel Silver stand point one of his most notable films was Lethal Weapon. I'm not saying it was expected to blow up huge, but it was expected to help steady a rocky ship which it didn't do. Without that it did create a question of what's next that can help steady things.
As said Sherlock was always being worked on, but you can see the cause/effect/push from the fall out of the disappointing box office return from Nice Guys. That focused even more urgency on Sherlock which probably began as more and faster drafts and when that wasn't turning up exactly as wanted this move was decided to be the next best step and because it's news worthy it's just coming out now. As said, each script draft isn't written about in the news. Just big pushes like this. So that speed up to this didn't make the news.
I can definitely feel that the tension over what's next was there. As said, I knew this Sherlock news story (not this exact one, but something) was gonna follow sometime after Nice Guys to signal a big push forward out of necessity. And that definitely is this.