Hi. I am a huge Trekkie so I just imagined a Star Trek expansion and thought up some elaborate thoughts on how it would go.
Firstly, you'd be able to have phasers, replicators and tricorders. I can imagine that a Sim holding a tricorder would be able to choose what and who to scan and it would be a good way to tell if, for example, someone is sick. And you could use replicators to make things. Phasers, I imagine, would only be able to be set to kill under a particular situation to avoid people being murderous, and, once stunned by a phaser, a Sim would go unconscious and have a slight drop in the Fun meter when they wake up but nothing too significant.
Also, you'd be able to choose what species your Sim would be and go through a long list of Star Trek species (would be quite long so you might have to scroll). And some species might have different needs, etc.
I imagine that Vulcans might not express emotion the way other Sims do and will not experience moodlets such as "need to brood". They also would be immune to death from emotions, but might go through some sort of pon farr every seven Sim years. When creating a Vulcan, you might be able to select the trait Able to Meld, and a Vulcan who is Able to Meld has the option "meld with" any species, and both the Vulcan and the other person might have a "melding" moodlet if they're melding.
And I think that Changelings would have the options "shapeshift into" and "become liquid" and would have no needs but automatically become liquid every 16 Sim hours, so the game might warn you if that's about to happen.
I think that Androids would have no needs and not have emotions, but could have the option of trying to express emotions, or maybe they could get emotion chips. They might also have the option of being damaged and needing repairs or being turned on and off, but I doubt they'd get sick.
I'm not entirely sure how Ocampans would work, but I can imagine that they'd have randomly-selected telekinesis/esp that'd be a bit unreliable, and that they could only Try for a Baby once and they'd age faster.
I reckon that Holograms would have no Hunger, Bladder, Energy, Hygiene or illness but would have emotions and would require mobile emitters. They could also be turned on and off.
Not sure how Trills would work, but joining might be an option for them, kinda like turning into a vampire for humans.
And that's how I imagined it. Probably won't actually happen, but fun to imagine.
