Even though I didn't like Tsuranga, I'm surprised the AI tanked so significantly. I'm wondering if there's something behind it. With Heaven Sent, the AI dipped because there was a massive generational split and older viewers didn't like it. I'm wondering if the pregnant man genuinely pissed off older viewers or something.
It could be that, but I also think Tsuranga's low AI is a consequence of the show's new attitude/direction. That is to say - generally speaking you can have a really shit episode (like, say, Fear Her or Curse of the Black Spot) but it'll get by on AI because it's got a cool-looking monster, or pirates. Or, like, the Adipose were silly, but Partners in Crime definitely gets by on a combination of the Tennant/Tate comedy and the heartfelt scenes with Wilf. My point is like - there have been a lot of episodes comparable to Tsuranga in the reboot years, I think, but because the Chibnall era is shaping up to be less sharp and witty and doesn't barrel along at such a "ah, forget it and just enjoy the ride" pace, people can linger on what's uniquely crap about it more easily and that results in lower AIs.
My tldr is just to say that I think the show's new tone means that worse episodes are more easily exposed as such, whereas sometimes a stinker could trade on bombast alone under RTD and Moffat.
Daleks for Christmas/very early S12?
I still think it's likely we'll get New Year Daleks, but I think the whole pitch for Series 12 is likely to be "LOOK! Old monsters!! Campy monsters!!", as that seems to be the most common criticism.