GTA 6 will be GTA WORLD, online only

There are some rumors and speculations that GTA 6 will not take place in one city, but instead will have every GTA-verse city (and maybe all Rockstar cities too, like Bulworth and Carcer). More cities will gradually be added on as time goes on. However, all game modes are online. I’m not sure if it will feature any new original cities, or if it will have the RDR cities but modernized.

Apparently this is partially why the game has taken so long to come out. Some Redditors think this is also why Bully 2 got canned: their work was combined into GTA 6.