Yeah, I like your idea under the spoiler.
The Master being in the vault appeals to me, might also be related to the classic series style Cybermen we've seen in the trailers.
The ladies of the Verity! podcast have had the same idea as me, or at least one or two of them did. Which makes me happy in a strange, sort of vicarious way.
Hadn't considered the Cybermen might be connected to the vault, although we've had vaults full of Cybermen before. Also, isn't the vault supposed to have Time-Lord style reliefs (circles and clocks, etc) on it, suggesting it's something they want hidden? The Cybermen were never really the threat to Gallifrey that the Daleks were.
I think it really has to be a female doctor this time - Olivia Colman anybody?
I don't know. I like Olivia Colman, but not sure I want her as the Doctor this time out. As for Ms Atwell, well that would make me really uncomfortable. I don't want to think of the Doctor
that way.
What I've been hoping for is that they get someone no-one is expecting. Doesn't matter if it's a man, a woman, what colour they are, whether they have an extra leg and a unicorn horn, just as long as it's someone no-one has put forward on one of those "Here are 10 people we insist play the next Doctor or we'll cry!" lists. All I require is that they can act well enough to play the Doctor. (Keeping in mind some bits are relatively constant, and other bits need to be new and fresh.) What I don't want is a badly written or poorly acted Doctor. I also worry that we'll be subjected to lazy writing with cheap gags about "Ooh, the Doctor's got tits, now!" Hopefully Chibnall will stop that kind of thing getting into the scripts.