As someone who doesn't do too much GUI programming on Linux, I find QML quite useful, actually.

Small effects and simple state switches ("disable/hide this group of inputs when the user disables the 'advanced' checkbox") can be written in simple code. The advanced plumbing (custom control rendering, window management) is left to native code.

There's a delicate balance there that I can imagine will be difficult to maintain long-term, but many applications just need a handful of buttons and maybe a text field somewhere to do their job, and that's where QML shines.