Redditor ImaPepper1885 has created the above image to imagine how the map would look if new islands were added to Grand Theft Auto 5 as DLC.
Last year, Rockstar North president Leslie Benzies told CVG that the game would expand "forever" and that they were tinkering with "old stuff" but he was likely talking about GTA: Online.
The consensus however seems to be that when the next Grand Theft Auto is released Rockstar will add the GTA5 map to that game's online mode to create a huge game world.
Anyway, it would be interesting to speculate on how it would all work and whether it would even be worth adding these islands to an already massive game.
It would be a lot of work too, but perhaps even if Rockstar aren't interested fans will be especially when they get their hands on the PC version. Skywind is one such massive mod project so we'll see what happens when Grand Theft Auto 5 comes to the platform later this year.