This repo is great proof that React is over engineered. Vanilla JS has WebComponents[1] and Templates, and a vDOM is easy to support (it existed long before React) and the DOM was the original place to store state in custom properties that you could manipulate internally with 'this'. What's missing is the ecosystem of Reusable WebComponents (primatives) based around this simple approach.
That's why this is so great to see. As more of a purist, I would try to make this a Vanilla JS lib instead of TS and remove one more build step. But the idea of 60 lines of code that use primatives (thus making this hyper extendable) is perfect.
[1] https://developer.mozilla.org/en-US/docs/Web/Web_Components