Regarding XML defined components: I have interrupted my work on the prototype to wait for decision from qucs_s-discussions-876 As a already mentioned: Using XSD with code-generation the client code can become very tiny:

try {
    std::unique_ptr<component::xml::Library> library(component::xml::Library_((modulePath + QDir::separator() + module).toUtf8().constData()));
    const QString libraryName(QString::fromUtf8(library->name().get()));
}
catch (const xml_schema::exception & exc) {
    std::cerr << exc << std::endl;
}

This is all you need to code to read-in, validate, and read-out (library name) from a XML-defined device. The whole work behind the scene is done by generated code as well as open-source library.