Rockstar appears to have set up DLC plans ahead of Grand Theft Auto 5's release early next week. The DLC comes in the form of special weapons that will be made available on the Xbox Live game store, with plenty of placeholder space at Ammunation, seen below:
As you can see, the description under the Ammunation menu on the top left reads "Visit the Xbox Games Store to find new downloadable content," all of which can be seen in a further screenshot:
Fans of the studio may have a hard time coming to terms with Rockstar's decision to nickel and dime customers for weaponry in the same way that other games, notably Just Cause 2 and Saints Row 4 have with additional weapons. It remains to be seen whether the DLC will be worth it to purchase.