Gintonic,
Your modifications to the Universal.hx file worked really well, however when I tested on a Samsung galaxy S4, it didn't scale right.
So I did some digging around inside Universal.hx and found the code that forces the "LetterBox" effect. All I did was comment this code out.
Now when I select "Scale to Fit (Letterbox), I get the desired result without the Letterbox effect, which means I can control the look of my game completely.
It would be good if Jon and the crew had an option to tick or un-tick the letterbox effect. But for now this is working fine.
Here are the lines of code inside Universal.hx (almost at the end of the file) which I commented out for your reference:
//Clip the view
//#if(mobile)
//if(!usingFullScreen && !stretchToFit)
//{
// scrollRect = new nme.geom.Rectangle(0, 0, scripts.MyAssets.stageWidth, scripts.MyAssets.stageHeight);
//}
//#end
//#if(flash || js || (cpp && !mobile))
//scrollRect = new nme.geom.Rectangle(0, 0, scripts.MyAssets.stageWidth, scripts.MyAssets.stageHeight);
//#end