I really liked the mechanic in MOO (Antarans attack, planets die) and now in Stellaris (any of them, but the End is pretty spectacular) for some joker/crisis events to occur that require some changes to the win condition (just survive, baby) to spice it up. I realize this isn't a balanced mechanic and makes games have a RNG quality, but since I'm not playing multiplayer, I would like some disruption in the end game.
Is there a mod that does crises or introduces events that the different civilizations have to work on (the Dread Lords or Arnor "return" and beat up civilizations that are not of that ideology and force those of the like ideology to participate in ever worse actions)? The Kohr-Ah show up from Star Control and start exterminating everyone? A faction that causes approval and influence to catastrophically plummet to make a new civilization out of many?