With most of the speculation centering around this new GL using Empire characters to unlock and synergize with, and rightfully so given the first stage of requirements, I'm wondering if we aren't seeing the forest through the trees. The Empire was only one stage of Palpatine's Reign. In the current requirements, we have only one character that is exclusive to the Empire in lore. Also, for a character named "Sith Eternal Emperor" it seems like Sith would be his primary faction. I would not be surprised if any further requirements omitted Empire and his main team after acquiring him becomes more dependant on Sith.