A lot of things in the reshoots are designed for leeway, so, just… be prepared that things could go lots of ways.
Well, you would surely imagine a crafty writer with production experience already might have contingencies or plans that worked with the aging of child actors anyway. After all, Timelord kids gotta age or regenerate at some point, right…?
Come back in 40 years when people have retired, other have died, and some will just not give an f anymore.
Yes that would have been such a bittersweet, poignant moment to end on.
Honestly, my own, realistic request at this point is that Series 2 scripts be added here:
and when they are, that early drafts of the finale with the original ending appear. If we’re really lucky, maybe a clip of the original ending on youtube as well, the way they released a few cut bits of the series 1 finale, including the Susan part.
Honestly the episode is basically fine up until that point. It’s not perfect, but it’s watchable. It’s everything after that that it becomes unbearable
Fine 
12 poppys
Honestly, it’d be pretty easy for Poppy’s next appearance to be as an adult. Presumably she ends up on Gallifrey for Susan to have been there, anyways. (So probably would have access to a TARDIS.)
Won’t happen. Can’t have such obvious evidence going counter to the narrative that works for everyone, especially Ncuti re. his departure.
Clip of an alternate ending where he sticks about? The tabloids would have ‘Unearthed clip reveals Ncuti Gatwa dropped from Doctor Who’ printed up within ten minutes of that.
Yes, fine. Not good, but fine. I have a lot of notes on it and I’ll never EVER forgive The Skull and I still probably wouldn’t like it, but I don’t think I’d have hated it like I do now
No, Poppy has popped off…for good one hopes lol
Next you’ll be saying it’d be an equally easy and shrewd move if Susan united with the Doctor against one of the foes they’ve previously dealt with together alongside Poppy.
The truth of Eccelston’s departure came out eventually, counter to the narrative.
Well, the matter of the Press Office making up a quote did. Beyond that, I guarantee you that fandom distinctly doesn’t have the full picture on that two decades on.
Besides, that’s different. Everyone here - Ncuti and his team, the BBC, Disney, Bad Wolf - are all united on this one narrative, gain from it, and would lose face and face press trouble if it should break.
But Poppy is a 100% normal human child now, if she suddenly becomes Time Lord again it’s going to have to take a very big lot of explaining!
No one can definitively claim “won’t happen”.
That’s easy. Just have it turn out that the reality patching-up was imperfect, have it ‘slip’ again, and then shift Poppy’s timeline again. First two could be done in a pre-titles sequence.
Well, easy, at least.
Though it’d also be easy to explain a regeneration in that Tecteun got hold of Poppy and ran some experiments, studying how she regenerates when murdered a few hundred times and comparing it to how the Doctor regenerates.
That’d really be the easiest way to explain the Billie Piper appearance, too. Reality just goes all weird for a few minutes, then reestablishes itself in a new configuration.
I think I can regarding whether or not Writer’s Room is getting the original script & if the BBC Studios social team will be even allowed to see the footage of that original ending.
I mean, heck, all but one of the Jodie-era scripts on Writer’s Room are not actual production scripts. They’re post-production transcripts with bits of script direction jammed in in places. That sure hides a few things, I can tell you that.
All these ways of bringing Poppy back sound like a completely inelegant mess. So definitely something RTD2 would do 
“Faithful viewer, Poppy’s back. What a hoot!”
Yeah, was mostly hanging my hopes on how The Pilot has a first draft version there with a bunch of cut content. Though scripts for several episodes of that season are totally missing, too…