Spoilers on this page are unmarked for ease of discussion.
Fate of the We Know the Devil protagonists
They are subtly referenced as being one of the main impetuses for the research of Eversion, and some of the about Neith and the Celestial Mechanics ending offer some clues:- One alone doesn't have enough gravity to survive, but what about three together? Or more, given at least some of the other campers are hinted to have become Devils as well in the Golden Ending. This, at least would give them a way to survive. It's not clear if Devils would evaporate on Earth though, since Culture on Earth is so much stronger.
- Somehow, they went to or were pulled to the Lunar Gravity Well, maybe intentionally to try to guide the unwanted children to another way of being. This might explain the "flutter of wings" inside the Lunar Gravity Well that the narration describes in the CM branch of Saturn and Pluto's last meeting.
Uranus was the intended test pilot for Celestial Mechanics
Aside from the fact that Uranus is the only one of the planets that a protagonist doesn't use as a name across the two games, we also know that every person with a planetary name is also a pilot, though Mercury was benched. It'd stand to reason that would include Uranus. And to be the kind of person Iapetus would praise above all else might imply they're kind of an asshole themselves, along with being a Butt-Monkey literally shoved in a locker by Saturn.