Glad to see some agreement there. I'm interested in building an ECS-based approach for a UI system at some point. The Yoga layout engine (implements flexbox -- https://github.com/facebook/yoga/tree/master/yoga) seems to actually be pretty amenable to just incorporating as a `Layout` or `Flex` component, then you could have components for platform-specific renderings (eg. `iOSTextInput`, `AndroidTextInput`, `DOMTextInput` in wasm, ...) that could read from cross-platform common components (`TextInput`). A core aspect would also be a `Hierarchy` component that just has a parent entity id and a list of child entity ids (that it keeps in sync properly). Then bind things to JS and allow you to code it from React, while still being able to eg. run an animation thread for some specific animations that just queries and reads/writes the `Layout` and `AnimationSpec`s etc. Interesting talk re: data oriented design for a webby animation engine here actually: https://youtu.be/yy8jQgmhbAU?t=620