My thinking is that we've had so much intrigue around the Doctors past, that a face from the past makes sense. Plus, we have the scene about telling people that you love them just before the regen, so maybe the Doctor is attuned to their past and lost loves in this instance.

That said, I like this theory - Doctor/TARDIS interwoven sounds like a really fun idea

I kind of assumed it was referring to the "threefold deity of malice and mischief and misery" from Harriet Arbingers speech in The Legend of Ruby Sunday last season.

As far as we know, Jinkx and NPH haven't filmed anything more than the scenes we've already seen, so the likelihood of them popping up is very slim.

Very much disagree here. While the arc was clearly a commentary driven plotline, we saw Ruby continue to struggle with life after the Doctor, and found something of comfort - someone who understands (albeit as a pretence).

Kate's behaviour was intense, but she is Mama Bear of UNIT and of Ruby. Seeing the damage Conrad was doing to her people, she was furious , and when he insulted her father, she snapped. It was a very human performance, and I think the point of the episode was to highlight the flaws of humanity - trusting the wrong people when we are wounded, letting our emotions take charge, and being so stubborn and unwilling to compromise our ideologies even to the risk of dying. These are such core issues for all people, and that's what made this episode work.

The visceral loathing I felt when Conrad unmasked himself was a testament to how well the ideas were delivered