For anyone interested in more details about React Fiber, the recommended links in [0] provide a great jumping-off point. For many apps, especially ones that render large amounts of data to a screen and haven't done (or can't do) much optimizing with componentShouldUpdate, it will likely be an almost-seamless drop-in upgrade that will make things feel truly more "snappy." A video (of a demanding stress test) is worth a million words: [1]. And it's coming soon: [2]
[0] https://github.com/facebook/react/issues/7925#issuecomment-2...