Being on an in-house team creating a design system and wrestling with many of the politics and ups and downs that brings, I can’t fathom how a design system built in isolation by outside agency could be successful.
Organization Y hears about design systems and how they solved the challenges of Organization X. They want to get on the bandwagon as well. Agency Z sees this as a money making opportunity and sells them a team of designers and developers who will design and build the system for Organization Y.
At no point does Organization Y consider, nor is told, that for the design system to actually work, it needs to be an internal product owned by the organization, not an outsourced project.
If your company can’t afford to have a dedicated in-house team to build your design system, please don’t farm the entire thing out to an agency. It doesn’t work. Instead see how you can partner with an agency to build a system that allows the future users of the system to feel a sense of ownership.