I'm hoping if it's not an expansion, the Crystal Palace is the setting for Cyberpunk 2078 with V as the protagonist.
I am of the opinion that when CDPR had plans to announce the expansions directly after the release of the game that they were going to announce more than two - given that they said there would be "as much or more" than the Witcher.
I think Phantom Liberty was one of those planned expansions to really flesh out Night City. I think there may have been another Night City centered expansion as well.
But I really think a certain space casino was going to be the setting with a certain Edgerunners lady-character hanging out at it was going to be expansion two or three - a post ending expansion, most likely.