Now, this isn't what I think the DLC will be, just what I think might be cool to have as DLC.
Consider a scene starting, explaining it was Friday evening, everyone was rushing to leave LC to go to the fictionalised Hamptons, to get away from it all. Then you are seen getting into a share car, arriving at the border for the Hamptons. When in the car, you get an invite to the party by one of the people you're sharing with and you go along. Once there, you mingle and decide to run around the house. You see something happen and the people involved notice you and there starts the 10 hours of gameplay.
Just an idea. If you like on it, perhaps you could elaborate on it. The we can get our hopes up!