This is a pretty common feature in any GUI framework, the ability to put text boxes, labels, and combo's onto a toolbar. Qt Creator even does this itself!
It amazes me that Qt only has actions added with addaction supported in the designer. I would like to see addwidget added to the XSD UI schema to allow arbitrary widgets to be placed onto QToolBar. It would be a straight mapping to the addwidget method of QToolBar.
The common use case of all is probably a filter QLineEdit on a toolbar, something very commonly used in a lot of programs. It makes no sense to have half of the toolbar be declarative in XML and then have to manually insert the other kinds of widgets through code. It breaks the dynamic capabilities of using a UI file to begin with.
Seriously think about it, why have only 95% of the above user interface from the Qt examples be declarative when it could be 100% declarative?
For these reasons, I would appreciate if someone could please look into this issue and see about getting it added.