I'm well aware of where Qt has (and has not) been able to run.
What I'm saying is that it's a lot easier to make new ports now than it was back then. This was mostly driven by Nokia's requirements, but it's still useful in the context of making a version that would run on Mir.
Qt has run on not-X since the beginning. It's always been available for Windows, and has had (suboptimal) OS X support for over a decade.