By this I mean Puerto Rico, the state of Hawaii, Guam, and so on. Or former american overseas territory like the Panama Canol zone, or the Phillipines.
There hasn't been a fallout game taking place in a tropical climate, all the previous games were in arid or temporate places. This could give an opportunity to show a different type of landscape, and new kinds of mutated wildlife. Which I would enjoy. The Phillipines would be too big to be a dlc though. But at least one of the Hawaiian islands could work, and the erupting volcanoes would certainly make for an immpressive looking landscape. Also the mountains reach high enough for snowfall, so with Hawaii you could still have a variety of enviroments with the beaches and coastal ocean, tropical forests, and cold high mountain tops. You could go to Pearl harbor as well and see the battleship Missouri.