We just got the episode titles for the two-part Doctor Who season finale...
And all I can say is, holy crap.
After building up the ‘Timeless Child’ it seemed a little odd that Captain Jack would suddenly show up mid-season and drop a cryptic warning about the ‘Lone Cyberman.’ Now it seems like maybe they’re one and the same?!?
And if that’s the case, and the Cybermen eventually ascend to become the Timeless Children.... it sounds like Chibnall may be taking a stab at semi-adapting Grant Morrison’s 1987 DWM comic strip The World Shapers, and taking the Cybermen’s ongoing obsession with “upgrading” themselves into the perfect species to logical extremes, and have them eventually turn away from surgical and mechanical grafts to biological manipulation, editing and rediting their genome, until after a million years or so of tinkering (possibly aided by time travel) they no longer look like Cybermen at all and have transformed themselves into the perfect self-renewing life forms... Time Lords.
That would certainly fit the bill for one hell of a secret the Time Lords didn’t want anybody knowing, why the Master went apeshit and destroyed Gallifrey,
and why The Doctor would need any sort of warning at all about not giving the Cyberman what it wants, when... let’s face it... why would she?
It still doesn’t explain how Ruth came to be, unless our Doctor somehow creates a paradox that causes Time Lord history to change. A bit like Hitchhiker’s Guide to the Galaxy when the Golgafrinchans crash land on Earth and cause the cavemen that were part of Deep Thought’s original programming to die out, but then end up assuming their place, so the ultimate question is still fairly close to how it originally would have turned out.
When time is ‘swirling around the Doctor’ it may be that she’s the lynch-pin around two different timelines, one where the Cybermen eventually become Time Lords and one where natural Gallifreyans eventually become Time Lords. Perhaps it’s even a double paradox, where our Doctor does something to cause the Cybermen-turned Time Lord timeline to exist, but Ruth (who’s from that timeline) does something to reverse it back again, with both versions sort of cancelling each other out, similar to the Big Finish story Flip-Flop, which can be listened to in either order.