Great question. So sorry for the confusion- I only used jQuery UI as an example, but perhaps it wasn't the best one. I'm trying to create a UI component library in vanilla JS/CSS that can be extended for use in React.
I guess I'm essentially asking: if I were to build Material Design, knowing full well I'd use it later to create something like Material UI, are there any recommendations out there for building the vanilla lib to make sure I don't shoot myself in the foot integrating that vanilla lib into the React lib?