Ubuntu – Using AppIndicators with the Qt framework

I think that the need here is actually more determining of the python-appindicator library is present. If it is present, it will support all the fallback cases that you need. It will handle XFCE, KDE and older GNOME appropriately. Good example of how to do it in this answer.

The appindicator library will use DBus to check if the application indicator rendering process is available. This will be the case on Unity, or if the indicator-applet is running. If it is available it will use that, if not, it will fallback to using a GtkStatusIcon with the same menu.

Unfortunately, I believe you'd have to keep both code paths if you want to handle the case of the library not being available. Though, we'd be happy to help get the library in other distros :)

Unfortunately, appindicator doesn't allow adding custom widget, as it requires GObject introspection. This will be available when ido package will have GObject instrospection.

Bug report