First reported by Insider Gaming, users on 4chan have shared assets purportedly originating from the 2021 CD Projekt hack that show a lunar surface area either cut from Cyberpunk 2077 or intended for a canceled DLC.
The initial post characterizes these images as coming from a canceled DLC that would have taken place during a new "corporate war," and compares its scope to the Witcher 3's Blood and Wine expansion. That interpretation, as well as the images' provenance, should be taken with a grain of salt, but the extent of what's on display, including an out-of-bounds view of one area that includes Cyberpunk's HUD, leads me to believe they are legitimate.
The thread includes screenshots of file directories: the parent file is "02_moon," and it contains folders like "arisaka_lab," "cosmodrome," and "bomb_crater_set." A map mock up indicates the moon area was planned to be six square kilometers, or about a quarter the size of the base game's map, with areas like an "NC (Night City?) Base," "HR Settlement," and the enticing "Drug Lab."
The most exciting map feature ties into that bomb_crater_set file: an "Exterior Movie Set" that sounds like the perfect staging ground for a Hollyweird/braindance-focused sidequest like the base game's standout Sinnerman. The thread also includes some prototype building and area designs, with one of the most fleshed-out models looking like one of the mass drivers of Cyberpunk lore.
Whatever this area's intended context, it couldn't have been very far along in development. Aside from the piecemeal assets on display, the CD Projekt hack it supposedly originates from occurred in February 2021, shortly after the launch of the base game. The thread also features two images of what appear to be early versions of Phantom Liberty's Dogtown.
Moon colonies and the various shenanigans corporations are cooking up there feature heavily in Cyberpunk's lore and 2077's story specifically. Characters in both the Edgerunners anime and Phantom Liberty are keen to escape there, the Corpo origin involves an assassination on members of the European Space Agency, while the Star and (Don't Fear) The Reaper endings tee up V staging a heist on a satellite casino. A starward turn has been a frequent topic of speculation for potential Cyberpunk DLCs or a sequel.
Late last year, CD Projekt Red narrative director Igor Sarzyński said that the team never considered setting any of Cyberpunk 2077's DLC after the base game's endings, so a Moon Colony Bloodbath might have been an awkward fit in the middle of the game's story. If these files are legitimate (and they seem to be), it's an interesting peek behind the curtain of Cyberpunk's development, but I don't think this got far enough for there to be a sick Moon expansion to mourn or anything, and what we got with Phantom Liberty was pretty spectacular.