If that's perfect, then I'm a monkey's uncle. It's definitely more code and less ergonomic than the previous procedural methods. You can also see Rust's syntax bursting at the seams when they declare widgets...
if you're writing an application, it's generally ideal to have everything declared consistently in the same language. I'd personally rather not have to edit XML files by hand, and try to shoehorn XML-declared widgets into a Rust application.