tl;dr I built a demo illustrating what it might look like to add async rendering to Facebook's commenting interface, while ensuring it appears on the screen simultaneous to the server-rendered story.
A key benefit of async rendering is that large updates don't block the main thread; instead, the work is spread out and performed during idle periods using cooperative scheduling.
But once you make something async, you introduce the possibility that things may appear on the screen at separate times. Especially when you're dealing with multiple UI frameworks, as is often the case at Facebook.
How do we solve this with React?