Why
There are cases where developer starts a new project and designer then picks it up in Qt Design Studio. Without the wizard creating .ui.qml files, it's confusing for the designers to understand how a project should be modified/constructed so that they can do their designer stuff for the project.

What
Optimally the project would also contain skeleton for c++ / qml integration in addition to .ui.qml files.
In Qt Design Studio new projects are always created with the .qml, .ui.qml and c++ files. The same wizard could be considered to be used in Creator as well and call it e.g. Qt Design Studio compatible project creation wizard.

As a sidenote .ui.qml project wizard was removed from Qt Creator in QTCREATORBUG-27085 since .ui.qml files were not possible to open in Creator. However, we have now capability to launch Qt Design Studio from Qt Creator so this shouldn't be that big of an issue anymore.