Fallout Lonestar.
Set in the central Texas wasteland this game (like GTAV) would follow 3 protagonists each with their own story and fallout 4 sized landmass to explore. The story would be closer to Game of Thrones than the typical fallout story. Throughout the games interweaving story the player would switch POV characters.
Character 1 would be a vault security officer chosen by the vault's AI to trek across central texas and find a vault tech bunker capable of unlocking the vault so that the inhabitants inside (including your family) do not suffocate from lack of power and air. Expect typical Vaultech high jinks as the savior, and their companion. a very recognizably named courier, visits Crater Station (College Station), Washington on the Brazos (Capitol of the Republic of Texas) and eventually the outskirts of an irradiated, and sunken, Houston, Texas where a mysterious super mutant army is forming.
Character 2 would be a Brotherhood of the steel initiate stationed out of what is left of the last free city in the south, Waco, Texas. An uneasy truce between the Republic of Texas and the Brotherhood has given the tech hunters the time to search for a hidden bunker of technology located somewhere near Ft. Hood. Join them and rise up in their ranks while fighting off the invading Legion that seeks control of Texas and its salt water ports.
Character 3 would be a Texas Ranger that is fighting off gangs of roving bandits funded and kitted by the Legion in an effort to bring stability to the area. Eventually uncover the Brotherhood's plan to plunder Ft Hoods tech and undermine their treaty with The Republic of Texas. This conflict comes to a head at the Battle of Three Armies as both The Republic of Texas and The legion lay siege to the Brotherhood Forts in and around Waco while simultaneously fighting each other.
So yeah, only the most ambitious video game ever made
.