I am not a designer (not for 20 years now) but that desktop image (rotating gif of different styles) is not a good advert. There are many, many layout issues with those that I would really spend time to try and make "default" look right out of the box (and in line with platform HID guidelines). I am a Rust developer, and I think Slint could be amazing, but those things will put off people who are driven by design quality.