Actually, I have to disagree, even as I agree I would be perfectly happy with the kind of things that would get that kind of rating, at present.
First of all, realistic sexual intercourse (in all the meanings of that word) definitely makes a setting and story more realistic, and it's for this reason that I don't like to see games, novels, etc, where it is glaringly obvious by its absence. However, a game that has "realistic, fully nude, sex" as a selling point is actually appealing to a juvenile audience, and tends to attract that audience, along with the negative repercussions of it; something of a paradox. And, sadly, we live in period where the US perceptions of what is appropriate, and thus how ratings are applied, is very peculiary skewed - extreme violence may not even get a product rated as unsuitable for children, especially if it is "normal" violence, involving firearms, whereas sexual content of any kind, but especially content that steps outside of "wholesome, man with one woman" boundaries certainly will. CDPR, and thus CyberPunk 2077, has to deal with the reality of this situation and the fact that a huge market is the USA, UK and other nations that will rate in a similar manner.
On another note, I would prefer that the time spent crafting a fully detailed sex system be spent on other aspects of the game, such as variety of aesthetics, depth of writing, and so on, so long as sexual content is still treated in an appropriately adult manner. I am fine with a character being able to pick up a street prostitute and go to a back alley, for example, even if I don't get to play a minigame of doing the deed, because the ault aspect of this scenario is not "roleplaying banging a hooker" but rather the acknowledgement that in a dystopian metropolis, you can be sure there are sex workers on the streets, legal or not. Equally, I am happier with the ability to casually engage in "sex" (with a simple cutscene, fade to black, or whatever) with an NPC, than I would be with being forced to only interact sexually with specific crafted characters, even if they had super-detailed, high resolution, fully realized sex scenes for that. For me, that's because it's realistic and "adult" to acknowledge that in this world, my character might seek out casual, relatively "meaningless" sex, purely for entertainment and relief, whereas it's a little bit silly to me that my character would only have sex with some predetermined character, albeit in glorious, titilating detail. I feel that the latter belongs in a totally different genre of computer games, which I am quite happy to see exist, but which are not CyberPunk 2077.