qmlscene is a developer tool, but it is not great as an app launcher. It would be worthwhile creating an app launcher which is better than qmlscene:
1. integrates better with unity. For example, it does not seem possible to run a QML app with qmlscene and specify a Launcher icon for it, without "installing" the app by copying .desktop files into specific hardcoded directories
2. is better documented: qmlscene has no man page; the --help text does not mention the --desktop_file_hint option at all
See also http://qt-project.org/doc/qt-5.0/qtquick/qtquick-qmlscene.html ("The qmlscene utility is meant to be used for testing your QML applications, and not as a launcher in a production environment. To launch a QML application in a production environment, develop a custom C++ application or bundle the QML file in a module.")
All 'qmlscene' tagged bugs regarding the wrapper: https://bugs.launchpad.net/bugs/+bugs?field.tag=qmlscene
With using only qmlscene you have also no way of changing the user agent string that is being used e.g. by XMLHttpRequest and XmlListModel.
Building an app launcher would bring the opportunity to maybe set the user agent string based on the app name or let the developer do it from QML.