One thing I'd like to see are Rust bindings for wxWidgets. Contrary to the prevailing opinion, I think wrappers over native toolkits are a fine approach for cross-platform development.
I'm not sure this is the prevailing opinion. It may be something of a "vocal minority" opinion, but it does seem more common in the Rust community than elsewhere. The closer you get to traditional native app designers and developers, the more you'll hear the opinion that native look & feel (not to mention accessibility) is important to embrace.
IMO an ideal solution is to offer both: 1. to wrap native toolkits for things like text and UI controls, and 2. to enable canvas-drawn virtual controls, for those who would prefer to create their own widgets. These approaches can be enabled in parallel through an extensible widget/component system.
Writing effective cross-platform application is harder than one would think. Some time ago there was a discussion on HN where a WxWidgets maintainer stepped in to explain why some WxWidget programs were apparently inconsistent across O/S, and the explanation was that they were developed naively (I think one needs to use specific spacing abstractions, but I don't remember with exactness).
For my personal development, I use non-native (which is easier to develop), however, on large scale, it'd be a tough decision.
WxWidget was my favorite in the past (again, for personal development), however, the bindings are very spotty, which prevents adoption for several languages (wiki page: https://en.wikipedia.org/wiki/List_of_language_bindings_for_...).