Either a full-blown major faction, or an option for custom factions where you start off with 5 or more pop types (major or minor) and exists as a democracy or federation at start. Think, The Federation from star trek, the Republic from star wars, the commonwealth from GR's Andromeda. A group of different races workng together for a common good. You get to choose which pops you get... or maybe you don't. I'm just brainstorming here people!! The use of certain pop types to colonize certain planet types. Multiple different types of ships possibly form the member factions.