In this modern era I think many people want to use smart pointers instead of raw pointers, and so it would be neat to be able to expose them to QML, like so:

class Test : public QObject
{
    Q_PROPERTY(QSharedPointer<Theme> theme READ theme CONSTANT)

private:

    QSharedPointer<Theme> m_theme;
}

The only alternative I see right now is to have a private function which just returns the raw pointer, which doesn't look too good.