They never really needed React in the first place, because React doesn't solve THEIR problem. Their problem is so specific to text editors: how do you get hundreds of lines of hundreds of rich-text characters to render as fast as possible?

In terms of game engines: React is comparable to the occlusion culling capabilities of a 3D game engine (render less), where Atom was in search of the fastest way for the graphics engine to push triangles to the GPU (render fast). Ultimately I believe a mix of both is the best.