In their latest Stellaris dev diary, Paradox said they have something large in-store waiting for players. They did not disappoint, with a brand new expansion and its release date being revealed.
The Overlord expansion's thematic focus is on exerting your will across the galaxy, the projection of power, and the expansion of civilization under your glorious banner. The other galactic powers can only choose to submit either willingly or by force. Beware that you are at risk of this happening to you as well.
In Federations, the developers expanded diplomacy between equals with the federations themselves and the politics of the Galactic Community. Nemesis included more hostile forms of diplomacy with espionage operations, and some empires declaring themselves more equal than others with the Custodians and the Galactic Imperium.
In Overlord, the exploration will be focused on diplomacy between empires that are explicitly not equal. The Stellaris Overlord expansion will be arriving alongside the Stellaris 3.4 “Cepheus” Update.
With this expansion, as is expected of something called Overlord, the vassalization mechanics will undergo significant changes. A major goal in this revision was to make subjugation a more valuable and viable system with benefits for both sides, rather than being a delayed “Game Over” as you wait for Integration should you be subjugated, say the developers.
In other words, where the Federation was the equivalent of the Star Trek universe, Overlord is coming dangerously close to the Warhammer 40k universe, and we love it.