I must disagree with your comment, I don't think re-creating React ( without looking at the source code ) makes you the React guy, the skills to be a good React developer, and the skills to be a developer that can create a framework like React I believe are not the same.

I think by creating a React-like framework what I will showcase is a deep understanding of the inner workings of the browser ( for optimization), the inner workings of React, and a good knowledge of languages and tools used to create this framework.