Popular data miner Tez2 revealed some of his takes on GTA 6. He believes that Rockstar Games plans to release single-player DLC with new cities and islands for the upcoming blockbuster game.
He also believes that new locations will be similar to Cayo Perico from GTA Online or North Yankton from GTA 5. DLCs will be connected to GTA 6 multi-player: Rockstar Games will add new heists to updated GTA Online mode with every single-player DLC.
Tez2 reminded that the studio developed single-player DLC for GTA 5 before its release — the community found the audio about Casino opening and some clues about Liberty City being ported to GTA 5 in the game files. He claims that both projects have been scrapped back in 2015.