I've been out of the GUI scene for a long time, but I will say I've been hella-impressed with some of the more modern Qt tech.
QML gives you JS for the view layer (and some logic if you desire), and a declarative way to lay out your UI. I think it's worth a comparison as a reasonable way to quickly iterate on a UI while having something very lean and portable as the output product.
Qt is a mix of LGPL for the core, and GPL for some of the "value-add" modules (for which there's a commercial license available for those who can't live with GPL requirements).
QML gives you JS for the view layer (and some logic if you desire), and a declarative way to lay out your UI. I think it's worth a comparison as a reasonable way to quickly iterate on a UI while having something very lean and portable as the output product.