> Rust is great and all, but every time I play with it I just don't see how it would work well with the complex inheritance tree that is a widget toolkit (meanwhile GObject works just fine, even if it's a little verbose at the C-level).

I'm not convinced that this is the best way to build widget toolkits rather than just how it's always been done. I'd like to see one built more on traits like IClickable instead of subclassing button.

HTML/CSS is already like this (for styling only), attributes can be mixed and matched.