Judging by the Dr Who 2026 Handbook cover, unearthly child Poppy was supposed to be a young incarnation of Susan Foreman. But then Disney and Ncuti had enough of the show, and RTD had to rewrite Poppy Chandra entirely. Phew!
So can we still appreciate the Poppy arc if we imagine the Susan intention was never a thing? Yes and this is how: Belinda met her child, Poppy, a year or more before she should have due to the Wish World. We met Belinda before she had Poppy. She was always going to give birth to Poppy in the show's future, on or off screen, with Ritchie Akingnbola as the father.
The only danger to her destiny was meeting 15 as by the time Wish-Poppy vanishes, she's ready to go on more adventures. If that happened, the one true Poppy would never exist. Only one could ever exist in Belinda's entire life/timeline at one time, no variants allowed. Even if the Doctor placed her back on Earth immediately, the damage to destiny was done. Ultimately, the Doctor's sacrifice brought Poppy, a 2-year-old, forward by 2 years.
Alternatively, his last scene with the Chandras took place in 2027, not 2025. The timeline got elastic to accommodate Poppy's existence and establish the canon timeline 15 died for! This all fits in with the RTD2 era theme of things happening out of order: bigeneration, 14's therapy, 13's cameo, Poppy's cameo in Story & the Engine etc etc