That line about being "The Doctor, the Original you might say" comes from the original Doctor, William Hartnell. So Capaldi was quoting his oldest version of himself while being attacked by a cyberman,

The final scene with Bill was too much like the final scene with Clara. Having the Doctor see past companions is what happened when Tom Baker regenerated into Peter Davison and when Peter Davison regenerated into Colin Baker. Nice touch, even if the regeneration hasn't been allowed to be completed yet.

Then at the end there that second person quoting the line about being the Original Doctor, is in fact the First Doctor, played by the same actor who played William Hartnell in a BBC documentary about him. History is repeating itself, The First Doctor didn't want to change and the now Capaldi's Doctor doesn't want to either. Of course by the end of the Christmas episode both will come to accept change. The funny thing is. the First Doctor regenerates after his first encounter with the Cybermen.

As for the Master. The Master has survived not being able to regenerate before. So even if Missy is never seen again at some point when somebody decides a new Master is in order, they'll come up with some reason why Simm's Master was wrong about Missy not regenerating. I think it was pretty stupid of Simm's Master wanting to murder himself just to spite the Doctor. Been then I've always thought this version of the Master was an idiot. I am not a Simms fan.

The episode for those of you who haven't seen it yet is about the Doctor looking for the lost 9th Roman Legion. He, and Bill, meets up with the Picts, and the Romans. The Doctor,
when he meets the picts makes fun of the weapons that the Pict Guardian, a woman, is using to put the enemy, a monster from another dimension, back to its dimension. After the Picts and the Romans meet, the Doctor says something that gets them to work together - protecting the dimension door to where the monsters come from. And so the episode ends.

I thought the way they handled the language barrier was a good reminder that the TARDIS has other benefits. And, when you hear someone speaking your language for the first time, they usually do sound like children trying out something new.

The time dilation aspect of the ship allowed for the full spectrum of cybermen models to be shown. I thought the earlier ones were much scarier. I am glad Bill got a happy ending. The Doctor finally found out he was a good man, and I think he wants to die this way. Not have to regenerate and learn the lesson all over again. That is why he is so reluctant to regenerate. I think he just wants it to end.