Be careful when starting a design system when there's an existing product. It's easy to think of it as the creation of something new. You don't have a design system, so you're building something new, and then everything will migrate to it - easy!
The problem with this approach is that you greatly risk creating [[20220328112501-lava-layers]]. An existing product probably already has a design system, or at least, something close to one. By making something 'new', you now effectively have two design systems. The old 'unofficial' one, and the new 'official' one.
The unofficial system has a way of sticking around. It's hard to remove code that has roots. [[20221202011240-existing-code]] It's easier to copy-paste what's existing, easier to use what you know, etc.
Instead of dismissing the old, think of introducing a design system as engaging and improving the old. [[20220704124529-design-system-harvesting]]
That way, every step forward drives adoption. Every step forward is a success.
https://amyhupe.co.uk/articles/bringing-intention-to-design-systems/