Design systems represent a user interaction design and development approach that is currently of avid interest in the industry. However, little research work has been done to synthesize knowledge related to design systems in order to inform the design of tools to support their creation, maintenance, and usage practices. This paper represents an important step in which we explored the issues that design system projects usually deal with and the perceptions and values of design system project leaders. Through this exploration, we aim to investigate the needs for tools that support the design system approach. We found that the open source communities around design systems focused on discussing issues related to behaviors of user interface components of design systems. At the same time, leaders of design system projects faced considerable challenges when evolving their design systems to make them both capable of capturing stable design knowledge and flexible to the needs of the various concrete products. They valued a bottom-up approach for design system creation and maintenance, in which components are elevated and merged from the evolving products. Our findings synthesize the knowledge and lay foundations for designing techniques and tools aimed at supporting the design system practice and related modern user interaction design and development approaches.