[danabramov]

There was never a plan to enable async rendering in React 16. “Fiber” referred to a new internal architecture (which enabled fragments, error boundaries, portals, and now context). It was a prerequisite to exploring async rendering, but it was also important for the above features, and it shipped in React 16.0.

Async rendering indeed needed more research but we’ve been testing it internally for months now, and are getting closer to the point where it’s ready. I disagree with you that replacing a few often misunderstood lifecycle hooks with more concrete alternatives significantly raises the abstraction level.

We did anticipate that some lifecycle methods will be problematic (e.g. https://github.com/facebook/react/issues/7671 was filed over a year ago, or a few months before the first line of Fiber code was written).

We’ve thought about these issues for quite a while. Jordan (creator of React) started thinking about them about four years ago (https://twitter.com/jordwalke/status/500587022890061824).

We needed time to evaluate different possible migration strategies and experiment with them, and we have a good idea now of what they look like. We don’t have all the answers yet but we’re getting there, and are doing that in the open.