Endless Legend's The Forgotten was a fascinating turn in the game (infiltration specialists) and from a lore perspective they were unique.  But what if other species among the cosmos were translated/converted through more Dust/supernatural means and learned to drift among the stars, creating a hidden network of trading secrets and assasination options (say to remove a hero for 10 turns...).  


I know, ghosts have no business in a splendid scifi 4x game just as aliens had no business with Indiana Jones, but the function of Dust in this universe does have a supernatural/higher-dimensional quality to it and can bend those rules if needed.  From a lore perspective.   And would compliment the upcoming Espionage Major faction that is in developement.


Just an idea.