>But the problem here is not the suitability of languages themselves, the problem is the huge undertaking required to build a gui library which can compete with Qt, gtk etc.

Well, the whole Cocoa/QT/WinForms scope might be huge, but we don't even have good minimal UI libs -- e.g. with just the few basic widgets: buttons, text fields, labels, radio buttons, checkboxes, kind of what HTML forms can do -- and only very limited functionality (e.g. no fancy text formatting in the labels or whatever).

Tons of programs could be GUI-fied with just the above (sort of what Tk does, but decent looking).

Libui, which was on hn a while ago, looks like the basic minimal cross-platform gui library to me. And that's already got bindings to crystal.. I think most developers are searching for something more.

Yep, something exactly like that, with good documentation, and bindings for multiple languages, can go a very long way for lots of apps.

It's a huge undertaking because it's an undefined specification. No one really knows what a cross-platform UI library should look like. How do you follow all of the native app standards automatically? How do you handle updates and distrabution?