There are a lot of ambitious mods out there, and Fallout has attracted quite a few such projects. One of those is Fallout: London, but if you want to go to warmer places, maybe Fallout: Miami would be something. The team has been working on this Fallout 4 project in their spare time for several years now, and a few days ago a new trailer was released.
It doesn't show gameplay (although most people probably know what Fallout 4 looks like), but offers a glimpse of the different places we'll get to visit at Miami Beach. The mod will have a storyline to follow as well as side quests, voiced characters, new items and two factions: Nuclear Patriots and Enclave. The developers themselves say that the mod has the same scope as an official expansion.
However, there is no release date, as projects like this completely rely on how much free time the developers can devote to it. However, they say they have internal goals, but they don't want to share them yet. The mod will only be released for pc, due to its size.
More info on the official website.