having quickly glanced through the rulebooks, I'd say most of it is fantasy...
Sure, it's cyberpunk, a parallel fantasy futuristic world liked "politicaly and socialy" to ours in some way
The thing is, the game is still pretty "realistic" as it's balanced.
You can "finish" the game, being the ultimate cyborg and all.
You'll still have a guy, buying a badass gun on black market with armored explosive bullets which will kill you in 3 shots.
You can't be "invincible" in cyberpunk, even if you're the most skilled played ever, you just can avoid dying in a stupid way, but once you fuck with the wrong people, you'll have a really bad day.
Honnestly, since the game is gonna be "create your character, live your life in Night City and build your story out of it".
I'd be all for a "DayZ" approach, you get your character, play it and all, and since it's supposed to be a dangerous and lethal world, you die?
Create a new character and get on with it.
Then, there will be challenge, you'll start the game a few time, making different things each time (or doing the same, up to you), now you'll feel the street being dangerous and without mercy, you'll learn to "know" Night City, more than being the "bad guy no one want to meet" like in GTA, where you don't really care about consequences at all.
The multiplayer will actually be pretty cool if it follow those lines, because even if some kid want to piss off people with his railgun, once he'll have a few player on his back, he's dead, and have to get back creating a new one.
You're not the hero, you're just a person, so it could be a nice way to make if really thrilling, you don't want to get in a fight, and you'll have to use your brain more than your bullets.
Tho, an alternative would be having a character for your single player mode allowing save, etc..., and another one for the multiplayer (builded in consequences), in an open Night City, having to deal with other player, it would be a whole "RP simulation" if done well, and since it would be lethal, most people would tend to play fair, some will not, but they'll die too, so it's not a big deal.