Tbf, I would gladly take mutability or impureness over unnecessarily complicated approach. One example of it is the suspense api in react. Suspense uses a promise throw approach opposed to generators. Your code throws a promise and suspense catches it to render fallback until it is resolved.

You end up with few ugly situations. First, I hate that I have to wrap my components (what if you want different fallback for different components? You end up with many wraps), how my UI will render is not isolated anymore. I often end up returning loading view from the components as we as well using it as a fallback for suspense. It just feels wrong. I lack control.