at my last job we did a gradual migration from Angular 1 to React. Its similar to the path to Angular 2 really. React and Angular can live side by side... All we did was build an Angular directive that can render a react component in a subtree (that's easy), and a React component that could render an Angular directive (that's a little harder, but not that bad).

With that, we could put a React component anywhere in our Angular app, and reuse Angular directives inside of React until we got around to rewriting them.

That ended up quite smooth.