Been using QML for about 16 months, since it was in a development branch. I believe it has alot of potential for development of frontends and also I see it as a kind of a replacement of html which was created with static documents in mind, and then got aumented with other paradigms (css, javascript, dom, etc).

I feel the QML language is in a embrionary state yet, they are writing the use cases and writing the language at the same time, which will in time show some redundancies in the concepts they use now. Example: 1)there should be more (multiple) inheritance so that we could derive from QML elements like we do in OOP; 2) there was no ability to access the items ids like in a DOM tree.

But what sets a project IMHO is the ambition and the goals. And this team has both, and their work will deliver.

I haven't used XUL, but XAML on Microsoft platforms, and for that matter HTML, show that the basic concept can work very well. My biggest gripe with XAML is the heavy XML syntax, which it looks like QML ditches.

There is no implicit connection between the quality of the resulting user interface and the method you used to define it. If anything, having a nice concise, hierarchical way of defining a GUI should lead to better structured, more usable (uniformly spaced, resizable) interfaces than what you would normally get out of click-and-drop editors.