Certainly that rewrite was huge, and it is currently "mostly complete", but Bevy launching when it did helped stifle a lot of the momentum. However, it was picked back up again in November and is now mostly complete: https://github.com/amethyst/amethyst/issues/2517

From outside at this point, the rewrite looks like a mistake , given the lost momentum and the current state of the project, but maybe when they finally get it out it'll turn out differently in 6 months.