Two words... Star... Trek...
A full expansion pack, on a fully functional starship (either a Federation, Romulan, Klingon, etc., Player's choice). We'll also be able to build our own, like a massive house, on a 800x800 lot, since it would be for a crew of a 100 sims. OR maybe just the Player's quarters and key rooms that the Player works in.
We can live on the ship as a crew member.
New career; with 3 branches: Command Division (Gold/Yellow outfits): Captain, officer, pilots, diplomacy, ship operations. Operations Division (Red/Gold): engineers, security, transporter and communications technicians. Science Division (Blue): Alien plant botanists (should be able to tie into Strangerville), science officers, medical officers, historians (learning about the history of the alien cultures).
All of the alien species; Vulcans, Klingons, Romulans, Borg, etc (probably just cosmetic CAS objects as extra category features, so that we can have hats and sunglasses on Klingons. Possibly adding a subcategory for the Alien occult for the Star Trek species, so Klingons and the others that have special facial differences can have their own skin enhancements OR have the skin enhancements be their own category, like tattoos.
New objects; phasers that only work on stun, teleportation, holodeck, replicator, sonic showers, VISOR, tricorder, new research (ties into University, maybe High School too?), and experimental technology.
Along with a separately purchased game pack that allows us to travel to a new planet (similar to the Star Wars game pack)... perhaps to save Vulcan?
All of it would intertwine with the base game, so we can take phasers and teleporters back home!
All so that our lovable Sims can boldly go where no Sim has gone before...
(I'm hoping if there's enough interest, EA will go for it).