Regarding Jannah, I think it would be a bit of a pacing issue to introduce a seemingly random stormtrooper in the midst of the story in a way that could feel organic. Maybe a throwaway reference could work (a name drop for “TZ-1719” over comms).
You’re the guy who suggested readding the elevator scene with the troopers and Finn, where the trooper congradulates Finn. You even proposed having that same trooper be the first one to turn on Phasma if JJB adds “Phasma’s End” into the novel. The trooper could simply be changed to female, and we get to meet Jannah in TROS as usual but ties to this hypothetical whatever.
Yeah, that could work now that you say it. If JJB is willing to do this of course, because the conversation between “Jannah” and Finn would need a few trims and readjustments. What I was saying is that I don’t think it’s going to work is suddenly diving deep into the trooper’s backstory, motivation etc, as if the book was saying ‘Hey, this trooper’s gonna be relevant in the future!’. At most a small cue that hints at her survival (even if it was plausible some stormtroopers survived the Supremacy’s destruction, the deleted scene has Phasma finish all the troopers off before her own death).