1) do the yak-shaving and create a whole new GUI stack in Rust (which would be an absolute boon to the Rust community but will be a tremendous effort), or
2) switch to Qt (and basically become KDE)
Thinking about it, maybe Sciter (https://sciter.com/) would be an okay foundation to build a DE in (lightweight stack, flexible theming, solid Rust bindings). But then it isn’t open source (only the interface is, you need to pay for source access), so maybe not.