In the days of Fallout: New Vegas, you had to pick and choose which quests you would accept, who you were okay with irritating, and—of course—which faction you would align yourself with. Fallout: Miami is seeking to bring that experience back to the Fallout universe.
Fallout: Miami is a community developed mod that has quickly turned into more of a full-sized DLC—like The Outer World's Peril On Gorgon—than a mere change of scenery. Fallout: Miami will be based on the Fallout 4 engine and will also feature the Sole Survivor of Fallout 4 as the main protagonist, instead of creating a new character for the story.
How the Sole Survivor gets to Miami is a story of its own that you'll simply need to experience for yourself. What happens when you get there, however, is a different matter. During an interview with the lead writers of Fallout: Miami, we were told that—while you can shoot yourself in the foot with the various factions—you won't need to worry too much about accidentally locking yourself out of content.
"With enough infamy, you can shoot yourself in the foot when it comes to that faction's content. But you'll certainly know that's the direction you're headed in before you get there," said Ezra Wayne—one of the two lead writers. Gabriel Troski, the other lead writer, elaborated, "We have a big focus on player choice as well as how their actions affect the world around them. That is one of the reasons for the return of the reputation system."
If you are feeling squirrely, we are told that your range of choices will even extend to the point of being able to kill every last member of a faction—though you'll probably want to avoid that. "If a player decides that the best way to solve a faction's problem is to kill every last one of them, then sure, you can try that. However, players should not be surprised by the fact that, if they act like assholes, NPCs will treat them like assholes."
That exact scenario was a familiar scene in Fallout: New Vegas—the further you progressed down the storyline of one faction (making yourself look like an asshole to the others) the more you locked yourself out of faction-specific content. As with New Vegas, though, you'll have plenty of opportunities to back-track and try to smooth over relations with the various factions of Fallout: Miami. Be careful though, your faction choice will probably change the face of Miami forever—for better or worse.