(Tagging @countlessrealities because you asked me a while back about what potential wishlists I have. But everyone can poke me for a plot/AU they want to do with me *wink wonk*.
I'll certainly post more later and along the way as I can think of more specific plots that I'd like to explore. Usually I approach partners directly if I have muses-specific plot ideas tho.)
Potentially a Dead Space 2 AU? He will see constant hallucinations of Nicole during that time and attempts to finish building the Marker for her to 'make them whole again'. He is the antagonist and protagonist of DS2 because he's manipulated by the Marker's imprint in his brain. And if your muse tries to stop him, they might do so by either killing him, or helping him free himself from the Marker's grip in the end. Ellie can appear as a supporting role.
Post DS3 plot where he survived but Isaac died (which was apparently the plan once for a continuation that never happened). Whereas the DLC ending was just a hallucination, but he DID survive the fall. He gets rescued from Tau Volantis and runs into your muse either on a Space Station or on Earth during his recovery. His life in pieces pretty much at that point. Maybe your muse tries to help him pick up the pieces while he potentially helps them out with a situation in return? Idk, there might be shipping potential in such a plot too, depending on chemistry.
What if Murderbot, or Three by extension, decides to let its deactivation code go rampant? If all Company Units get to disable their GovModules and suddenly a HUGE load of confused and angry SecUnits end up on the loose? Would it end up in a mass-murder scenario as predicted in medias, or would the poor constructs just need a helping hand in finding their purpose in life after gaining sudden freedom? Maybe a rebellion/freedom plot for constructs would be interesting to explore, if your muse is the kind to free them from company enslavement.
I'd like to have more threads with Grum again in general, while preferably resetting previous relationships with them. I have been struggling back then with the way I want to portray them and most of the interactions were just... bad. I think I want to put more emphasis on Grum finding their own identity and purpose as they travel space but also discover Earth (and why the other Utrom are so fond of humans). They're still socially awkward and gloomy, but not in the amount that I wrote them back then.