I'll admit, one of the things that has been lacking in Stellaris is interactivity with your pops and the factions they create. Up until now, the only factions that can be created by your pops are Independence-seeking rebels under various names like The Joy First Committee or The Sildor Nationalist Party. But the 1.5 Banks update pledges to fix this little issue.
Paradox Interactive has said that factions will instead represent political parties, popular movements and other such interest groups. Most will only consist of pops of certain ethics, for the example they gave, the Supremacist Faction desires complete political dominance for their own species and is made up exclusively of xenophobes of that species. Not just xenophobes in general, but only for their particular species. While the Isolationist Faction could be joined by both pacifist and xenophobe pops regardless of species.
These factions will form over the course of the game, like they do right now. But as your empire grows and expands these factions will start to help or hurt your society. A happy, content faction will generate influence for you while an unhappy one might decide its time to push for independence. These factions will have issues they want you to take care of as well as a certain attraction level to pops that might not already be in a faction. Now, lets talk about Ethics changes.
Keep in mind, this update will be entirely free so every player is going to be getting it regardless, some time in the future.