BBC showreel that they just aired after episode for 2017 suggests otherwise. Which is a shame coz this series was fucking awful.
That was an old trailer, they didn't mean to imply there is more Sherlock coming this year. All the footage in that showreel (which again, was released earlier this year) was meant to promote the episodes we just watched. None of it was new. It just happened to be among those other new shows because it aired so early in the year and they didn't cut it out now that they aired. Sherlock is done, definitely for this year, at least for the next couple of years, possibly forever.
I liked it as usual, but some things didn't sit quite right with me. The room escape/puzzle element is fine, but it's a bit lackluster if this is really the last episode. And the brainwashing powers - eh. It would have helped if there was a scene where she convincingly drills down into someone's mind by talking to them, but the way they executed it here wasn't convincing at all. I can see them coming up with the idea and thinking it can lead to a good story (and it could), but the execution wasn't there and that makes the entire thing fall apart a bit. You can handwave logic away like that when the Joker takes over Arkham Asylum, but here it stood out a lot.
I mean, these people are supposed to be running the most secure asylum in the world. Sure, maybe someone like her can talk someone into being depressed or doubting reality, but surely they'd recognize she's fucking with them and someone would tell someone on the outside
something about what was going on in there. They acted like every staff member there was hypnotized or something. Like she had superpowers.