Random fact I just realised about this episode — the “spooky kid” Belinda saw in the alley as she was running through Lagos? She’s played by Sienna-Robyn Mavanga-Phipps, who was Captain Poppy in “Space babies”. The character is even credited as “Poppy” in “The story & the engine”.
Please don’t @ me about your great intense love (or otherwise) for “Space babies”… but let’s just sit for a second with what a deep, weird cut this is. I have no idea how or if it’s going to tie in with anything, ever.
I think there’s some potential there for this to be a one-off appearance that won’t be revisited. The Doctor did say “the stories were leaking out, getting mixed up.” So this could just be that and nothing else. Otherwise, who knows … Poppy for next companion? It does seem like a very odd inclusion if they have no intention of following it up.
If there were multiple callback characters leaking out of the story, I’d be more inclined to say it’s just a fun visual reference to see them again–and I guess it’s possible there are more returning characters hidden in the crowd scenes–but having just one character leak out and then do nothing impactful in the story points to them having specific intentions for the character in future episodes.
Per your request, I am withholding my excitement or otherwise for the prospect of more space babies.