Obviously Raph knows what he's doing, so this isn't a critique, but a question:

What's the reason for replicating the "React idea" outside the web browser?

The way I understand the motivation behind React is that it tries to work around the too high level and too rigid DOM by mapping one way to describe an UI (the React API) to another (the DOM), for the only reason that there's no realistic way to bypass the DOM (except doing everything yourself - including fundamentals like text rendering - via a 2D- or WebGL canvas).

But if you don't have something as rigid as the DOM as lowest layer to begin with, what's the point of building a React-style system with 'tree diffing' against data that persists across frames? Is it really worth the complexity managing intermediate data that sits between the UI description that (most likely) needs to be updated each frame, and the low-level rendering instruction stream - which most likely also needs to be generated each frame?

Or is it all about Rust's language restrictions?