I love immediate feedback but getting it ranges from hard to neigh impossible. E.g. I have a complex Emacs setup for rendering Pikchr diagrams, but there are a lot of problems to solve from diagram conception to the end result, so I thought, hey, why not make my own cool RT editor - in Rust obviously.
Unfortunately I learned that GUIs are though problem especially if idea is hobby-based so there's only one developer inside. Ultra responsive GUIs cool, I have a prototype in egui (not sure if that's as fast as Zed's premise but feels fast nonetheless) and yet it doesn't support multiple windows, which I wanted to have.
120 FPS with direct rendering sounds AWESOME just for sake of it, but I believe that for the end-user layout will be more important than refresh rate, and that's different beast to tame.
Personally I "almost" settled for Dioxus (shameless plug: [1], there's link to YT video) and I'm quite happy with it. Having editor in WebView feels really quirky though (e.g. no textareas, I'm intercepting key events and rendering in div glyph-by-glyph directly).