One of the roles of a transmedia creator is to develop the storyworld of a property, to ensure that it is big enough and rich enough to sustain stories across media, and to ensure that it has a consistent theme and tone. Last week, Chuck Wendig wrote an article about worldbuilding for writers, and I wrote an additive response. The gist was that worldbuilding is important, but only to the extent that it supports the story being told. The story myst come first in all ways.
In transmedia, we talk about the "storyworld" and I think this term is perfect for what we do, because it is equal parts "story" and "world."
While someone writing a novel must place the story before the world in all cases, someone developing a transmedia property needs much more focus on the world. The world needs to be able to sustain many stories, potentially including audience-created stories, and while a driving platform story might be known from the start of the process, one cannot predict every story that will be told in that world. In that way, the world cannot be slave to the story in all instances -- much world development must be done outside the scope of a current story.
Therefore, it may seem like the opposite holds true for transmedia creators over single-story writers -- that the world must come first. But, like I said, I think "story" and "world" are equal in that term.
When creating a storyworld, you can't be a slave to story because you don't know all the stories. However, story is still a vital consideration to make. If you're working with a primary story, a driving platform story, it should heavily inform your world. The story and world should be developed coexistently, drawing on each other. The world still needs to serve the needs of the story.
Furthermore, you need to build the world for the potential of other stories. You need to leave doors open for the future, seed possibilities, and leave enough blank space to be filled in by other people -- blank space that is designed precisely, such that when it is filled in, it will still work with the established canon of the rest of the world.
There's a lot more worldbuilding work in a transmedia project than there need be for a single story. The world needs to be big and rich enough to support endless stories -- but in that, it still needs to be aware of the stories that will be told. The world is less slave to the story, but the story still cannot be slave to the world. They must build off each other for a symbiotic storyworld.