If I could make one change to Metroid lore (I mean aside from small things like hardening the science a little and letting the world expand beyond the immediate proximity of Samus's life and dressing up the art style with one or two or layers of dirt and grime) it would be to add Chozo children. In the manga they talk about the Chozo race being in their twilight years, genetically incapable of weilding weapons and having all become infertile, which is kind of intersting, but... Unlikely? They're an advanced race, surely those are solvable problems? And even from a meta perspective... Why? That whole plotline doesn't go anywhere or do anything beyond just handwaving away why the games never have any Chozo alive. What does it mean for the themes of the franchise? Or for Samus? No other piece of cannon ever mentions any of it or expands on it, so it seems like a waste of whatever it was, and now the Chozo are just the Weird Old Guy species.
So anyway my pitch is that one could get a lot of mileage out of the Chozo still being a diverse, lively, functioning species. Either by including survivors somewhere, or if that's a little cheap, by giving some substance to the world that Samus lost.
She had friends. Kids she played tag with, went swimming with, fought with, who teased her for having hair. They explored caves together, had inside jokes, favorite foods. Some were older, some were younger. Some looked up to her, some looked down. She had a mentor and a crush and a sibling. Maybe she had a best friend. Maybe she had a comforter. Maybe she wasn't special then.
Maybe she wasn't special for a long time.
What hasn't changed from canon is that the Chozo had been on decline in the centuries since the heights of their galaxy-spanning empire. There's been an overreliance of technology and a fading of spiritual understanding, there's been betrayal by warmongers, invasion by barbarians, colonies winking out in the wake of a hundred natural and artificial cataclysms, whole planets disappearing without a trace and rusty robots marching back and forth with dried blood on their claws... But a spark of life and health and hope remains on Zebes, where the memories of the old ways run deep, and warrior training is maintained for tradition rather than conquest. The Zebes eldership knows that the flame they carry could do much kindness to a dark and hurting galaxy, but they also know that a well-placed genocide or two could snuff it out for good.
The recent loss of contact with the Thoha was the final straw; they would send out new warriors fully equipped. Anyone with wisdom, a pure heart, a gift for athletics, and enough neuroplasticity to survive the enhancements, up to and including that one foreigh orphan, was eligible to endure the trials, bear the ancient weapons, and roam about the galaxy protecting the innocent and bringing justice. The duties and equipment of the greatest warriors of the long lost generations would be theirs in the present, and the plasma-hot olive branch of the Chozo would bring true peace in space again.
They were a class of twelve, who trained together. The central AI oversaw the tech, Mawkin defectors mentored, the elders tutored. Most of them were Chozo, two were Ylla, one was human. They earned their power suits the same day, then left Zebes to study abroad. She joined the Federation navy's human branch, they went other directions, and none of them realized they would never see each other again. She finds the remains of them here and there on her travels, some bodies torn open by dragon claws in the very halls of Chozodia, some left nothing but self destruct craters, some found hopeless and lost on the surface of some moon having taken their own lives, one severed arm cannon found adrift in deep space with a mangled chozo hand inside it; no other clue for a million miles.
Samus, and the armor she bears, are famous far and wide. But if all were right in the world, she wouldn't be; there would be more. If the pirates hadn't come to Zebes, if the central AI hadn't betrayed them, if the Mawkin had responded to the distress call, if the Federation comm channels were just a little faster... Maybe there could have been as many as twelve. Maybe in a few years the next class would have earned their power suits, and there would be twenty-four. Instead, there's a debris field and a naked core where a world used to spin, and a legend shining where a tradition used to glow.
Instead, there's somebody special.