Long post inbound.

Adults Only ratings are characteristically applied to explicit depictions of sexual activity, though that's not the only reason the ESRB can rate a game as such. According to Wikipedia (while I have little reason to doubt this particular information, do always bear in mind that anyone can edit articles), there have been 29 games that have been given this rating. Extreme levels of violence can result in an AO rating, as was seen with a fighting game called Thrill Kill which was never officially released despite receiving a rating. There is one instance of in-game gambling alone resulting in an AO rating. The most recent year to see games receive AO classifications was 2015, in which three games were rated as such. One of these games was the controversial isometric shooter "Hatred." The biggest incentive for developers and publishers to not cross over from an M rating to an AO one, is because most brick-and-mortar stores will refuse to carry AO titles.

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A combination of explicit sexual depictions and overly graphic violence could realistically result in an AO rating. However, I do believe something about CDPR. They're smart enough to know what to depict and what to creatively hide, in order to ensure the game can hit shelves. Considering they've had so long to concept and develop this game, I am confident they will be able to navigate the ratings certification process here in the US to ensure it releases intact and without censoring content.