Sure there have been a lot of survival games. DayZ, Ark, RUST. Some (like RUST) have nudity, but nudity itself does NOT make it adult. It only is "adult" if you are in oppressive Middle-east, America and Australia. Everywhere else, its completely normal.
However, the part where the adult theme comes in is how bloody, gory and how X-rated the world of Conan is. No other survival game has exploding bodies with parts and blood everywhere. There is no survival game with as mature of a world as Conan. There is no survival game with blood. Kill zombies in DayZ? No blood at all. Kill animals or other people in RUST? No blood at all. Ark? As kid friendly as any game could ever be, Ark can be played by elementary school kids because how kiddy it is. When I tried Ark, it feels like I'm a pervert playing a game made to be as kid friendly as possible
Sure, maybe that in itself does not make a game. But the world of conan is savage. There are slaves (which is very adult oriented content, but many people in America will be highly offended by it, which is good as once certain News picks it up, free advertising for Conan. Imagine a parent lets their kid buy it and then sees they have a slave or multiple slaves? Imagine the shitstorm the news will make out of it), there is blood, sex, nudity, gore, blood, savagery...all that makes it the first survival game made for ADULTS. Not a kid friendly game at all.
I am VERY excited for this, though won't be buying it till next month (which is coming up anyway) because too low on money this month. The first actual adult survival game made for adults, not kids. Granted, kids will play it anyway and there'll be a lot of pissed off parents.
My Skyrim, Fallout 4, Starbound and WoW + other game mods at MODDB: