I have an idea on improving simple-xml in element/class sub typing. As far as I understand attribute "class" is used to mention subclasses of annotated class, for example:
If we shall have info about all subclasses of mentioned class we could omit "class" attribute in xml and use @Root(name) of subclasses. I'm not sure but think it is possible to add to @Element, @ElementList and @ElementArray parameter with list of all subclasses of annotating element class. In case of unknown subclass we can still use "class" attribute.
I think it would be great to improve readability of xmls that simple reads and writes.