One useful thing would be a style tiles component that would expose the visual nature of a theme and also its corresponding dark theme maybe even side-by-side.
These could be updated by modifying the CSS variables, but this is a very tech lead and approach.
A better approach would be a match set of style files for light and dark pain that could be expose stigma and allowed designers to change the colors more directly.
Then you could use Figma to build a CSS variables either through a plug-in script or copy paste by CSS output. In storybook, this would allow for rapid iteration and testing of basic theme colors and how they might articulate through a unstyled SHADCM variant.
also see kitchen sink