Steven,

I joined the Airbnb in October last year when the Design System project got started. Initially, I worked together with the team defining the basic style guide, like type, spacing, colors. After that, we worked closely together for a month of creating the new designs and defining the components.

Currently how the contributions work is that we work with teams that want to add something. We also ask them to submit a proposal on changes and a reasoning why they cannot use the existing components. We try to decide on how important is the use case and how universal the solution is. The best case is that the use case is very important, and solution is very universal (can be used in lot widely). When we find the request is sufficient, follows the system and our standards, we officially included into the component library.

We use git/github currently to facilitate the actual file updating process. We add the new components to our Sketch Library, work with the engineering to make sure we didn't miss something and submit a pull request with a changelog that document the changes.

We also Sketch templates that automatically update when update the design library, so all the designers have the access the the new files immediately.