As I said, it could be a standalone thing.
Right, but then it wouldn't be Cyberpunk 2077. It would be Cyberpunk Online or something - a completely different game built from the ground up... or maybe having some assets transferred over.
This doesn't mean characters, concepts, places, etc. from Cyberpunk 2077 couldn't be included. But it would be an entirely different game built on an entirely different engine... and it wouldn't be something we are getting any time soon.
Because of that the more realistic scenario is that we get Cyberpunk 2 as a single player game before they introduce multiplayer elements. That is because single player games are CDPR's bread and butter. They will use the big open world game to draw people in, then try to get them to play the online version of the game that will likely feature microtransactions, a cash shop or something like that. Just like they will do with The Witcher, most likely.
A good example is Bethesda and Fallout. They didn't release Fallout 76 to hype Fallout 4. They released Fallout 4 and then followed up with Fallout 76 afterward - a 'different game' but with a ton of similarities to Fallout 4 in terms of engine, graphics, assets used, etc.
I think that is the more realistic thing to expect. A 'Cyberpunk 2' single player game and then a multiplayer version or stand alone game that re-uses a lot of characters, assets, etc. from the single player experience.