Government reworks and Hive Minds
Traditional governments are being thrown out of the window in favour of Authorities and Civics.
Authorities determine who has the keys to your government (Democracy, Oligarchy, Dictatorship and Imperial Monarchy)
Civics determine aspects of your governments and how it is run. For example, one of the civics holds that only members of the military have the right to vote if you want to make a Starship Troopers/Helldivers/Turian society.
Civics are dependant on your governing Ethos and the authority of the government and can be made invalid through the course of the game. If this happens, you can reform a governemnt, like you normally would, and you'll be refunded your points to re-spend on civics and be allowed to re-choose your authority. Some civics can't be undone (such as syncretic evolution) and some civics can only be obtained through the course of the game.
A special kind of authority exists only with the Utopia DLC exists known as Hive-Mind. Hive-minds get their own unique form of civics but do not gain any benefits from ethoses. Their pops are not affected by happiness and as such, will only perform jobs as though they only had 50% happiness. Hive-minded pops cannot exist in non-hive-mind empires and vice-versa (They can genetically engineer non-hive-minded pops to be hive-minded like themselves and they'll be considered a part of the hive-mind ruling over them). In addition Hive-minds have immortal rulers but may not pursue any form of AI or psionic research or go down those ascension paths, they're also distrusted by other empires on first contact.
In short, Hive-minds have no internal troubles and never need to worry about nity or influence, but, have restrictions on how they play and can be outpaced by a well-managed Empire.