What features will actually be in the game?
This is an extremely broad question that I'm not entirely sure how to answer...the game will be a third person, action adventure with role play elements, horror elements and survival elements; the game will feature multiple customizable characters, loadouts, weapons, skills and vehicles; the game will feature both mission and free exploration, following an overarching story regarding the state of the planet you're "stranded" on, with the ultimate goal of escaping said planet by acquiring a ship.
For anything more specific either look at the other point or try to narrow your question a bit more...
How big is the game world actually intended to be?
Matto has created a planetary generation to procedurally create a "moon sized" game world; in order not to have this large world implode the engine (UE4), the world will be subdivide in "tiles" that cannot be traversed seamlessly, but there will be a loading screen similar in concept to MGS3 Portable Ops:
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, putting all these tiles together will create the game world (think of Helldivers 2 and how the planets are made of various maps that are all distinct while maintaining consistency between them, but instead of having multiple planets you have just one with multiple biomes).
The same system is leveraged for the more complex interior areas and general Point Of Interest (POI) that will be available across the planet.
What game modes will be in it?
The main game mode will be called 'Persistent World', where each major area will feature its own gameplay elements, one of these will be 'Groundzeroes', a free-for-all combat zone where players will take the role of a PMC operator and will have to fight to stay alive while completing specific missions that could turn the game into an Extraction Shooter for one objective, for example. Players can take jobs/operations and each type of jobs/operations will feature different kind of gameplay
A story mode, called Scenarios, is also being discussed, that will feature multiple shorter scenarios with different stories, all part of the same narrative.
When and how will H content be implemented?
Once enough assets and mechanics have been completed to be able to call the game a game, Matto will give the green light to Gato (proper adult artist and partner in crime) and provide assets for the creation of an Adult Module (referred as Adult Mod), this mod will be integrated with the game and will add upon the existing systems, integrating at various level while being optional, to allow the game more mainstream visibility and avoid being banned in certain countries, since Steam is the target release platform.
tldr: when? no official eta/when ready.
How much of that will actually make it into EA, how much is slated for the Full Release and what parts of it are planned as DLC?
EA is EA, and will receive updates on the go, Scenarios will most likely NOT be a part of release, while the adult mod will be released sometimes between EA and release and maintained alongside it.