After porting Qtopia Core to Mac OS X, the next step was clear:
Okay, it was a weekend hack, so no fonts yet (unless you prefer blocks instead of glyphs) and no qvfb (vnc is the only output driver at the moment).
The wiggly example in the screen shot is a native Windows application and does not link to any win32 UI libraries. It does all the rendering itself and exports it through vnc. This allows Windows developers to develop embedded applications and test the look&feel without running a complete OS emulator.
Of course, this requires some discipline while developing, but since Qt features a pretty complete OS abstraction (file system, sockets etc.), it's possible to develop a Qtopia Core application in a team with mixed OSes without too many headaches.
No source code yet since it's in quite an early stage, please send me a mail if you're interested in a patch.