It is what Makepad is working on in an interesting way using Wasm and Rust. They have created a Figma-like DSL and a good code separation with the logic behind it. You can edit UI's of in-production apps, and they are bundling an editor for that. Accessibility is an issue, and the project are looking to offer proper support there. In their video linked on the README they run the conference slides on Makepad with live apps embedded and running at 120 fps.
https://github.com/makepad/makepad
https://news.ycombinator.com/item?id=36567681