I think the tools they are letting us use will allow so many different types of "games within the game" to be made with it
I would imagine at one end we will see people making their own Strangerville stories and then at the other end we will see people making their own version of GTA using the direct control and over shoulder camera. With these tools you can easily make, -without any real programming skill-, GTA Convenience Store robberies for example. You could even make smaller scope stories such as murder mystery games of Cluedo within a mansion house with meaningful scripts.
The benefit of releasing all the creators is that the developers dont need to make gameplay "Expansions" although I am sure they will make at least one classicly regarded expansion yearly. They can just do "Item and housing packs" for different themes and time periods
