Here's my pitch for a better ecosystem: we develop an intermediate standard for fundamental UI building blocks (divs/blocks/layers, images, video, etc.) + a layout engine, sort of like the DOM. Shells (browsers, native platforms like React Native but without the React requirement, etc.) would give JS renderers access to the lowest level painting calls available (ie. "repaint this node") along with programmatic access…
I think Cordova could be leveraged at the very least.