Big caveat up front, I have no illusion that this was ever planned out, or that it's ever going to be made. I just connected some dots from Eccleston's season to our current mess. I do think that if the BBC had Pete McTighe make a 15 minute special along these lines and put it on Youtube, the fans could rest easier and the next production team might start on a blank slate.
To summarise, the last couple of seasons had a convoluted arc concerning a companion's parent issues. She was saved as a baby through time travel intervention, but not without a lot of temporal disturbance in the process. In fact, babies have been a throughline in both Ncuti Gatwa's seasons, a pattern that culminates in the Doctor rupturing the Time Vortex in order to save one child's existence. For just a probable moment there, that child is his own. Succeeding in his mission, the Doctor is then replaced by somebody looking suspiciously like Rose Tyler.
- Church.
- Baby.
- Rose.
- Temporal paradox.
- On what could be considered the Doctor's Father's Day.
Bring on the Time Reapers to sterilise the wound in time! That's why the Doctor regenerated into this face, à la 12 looking like Caecilius from "The fires of Pompeii". She needs to channel Rose as a catalyst to heal the reset 15 did to save Poppy. Besides, where Pete sacrificed himself to sort the timestream out, this time around the Reapers are attacking the Doctor and their police box. And the Doctor's current face has a very special relation to the TARDIS' living heart.
To be fair, the rest of the story doesn't really matter, this is only meant to resolve the Billie Piper twist of "The reality war". It doesn't fix fan quibbles over the Timeless Child or the Doctor being half human on their mother's side for a hot minute in 1996. Pretty much everything other than that latest regeneration cliffhanger can be ignored or picked up upon by future writers. So end this minisode on a regeneration without showing what happens next, or just leave it open ended.
Now, would I love for Susan to pop up for no other reason than to ease her "grandfather" into the credits crawl, and a future season where neither actress are seen again? Maybe an exchange to echo the Seventh's exit monologue to Ace at the end of "Survival"? Absolutely, but this could well be a one hander between Piper, some 2005 archive footage, and the janky old low-poly CGI monsters from back then.
[made a few edits for clarity(?)]
I guess it's not so much a theory as an unsolicited pitch, but whatever. Glad you appreciated it! I had a chuckle myself realising how well they could tie "Father's day" into the current situation.
And I genuinely think the BBC could sort a lot of it out with a relatively low cost Youtube release. Just clearing the board for the next writing and production crew.