What about relm4? Is it generally feature complete? Can one use relm4 for most things, and drop to gtk4 for the oddball task that is not supported?
I have to say however that despite heroic efforts by the authors, it doesn't really feel as nice as the "real" Elm architecture precisely because of the imperative focus of gtk-rs' API, the nature of Rust's memory management system, and depending on what you're doing you may feel forced far too often to drop from fantasy land to reap the benefits of the abstraction.
I'd still consider it next time I tackle a native app, but having tried Slint for writing simple UIs and having read some iced code, I think I'd only go for it if I'm really going for the Gtk native look and ecosystem.
What I am asking is, does relm4 have all gtk4 widgets and is generally feature complete? Is there any reason at all to prefer using gtk4 directly rather than the more ergonomic relm4?
As for feature complete, depends on your definition. It's on 0.6 and major changes do arrive and updates do break user code, but you certainly can write apps with it.