XPathFactory.newInstance() currently does not work. It seems proper redirection in __JAXPRedirected is required for it too.
Initial proposal from David (https://github.com/dmlloyd/jboss-modules/commit/1b21ce6) still does not work because the XPathFactory looks for system properties with the following name to get the implementation name:

String propertyName = SERVICE_CLASS.getName() + ":" + uri;

It's probably acceptable to set the "javax.xml.xpath.XPathFactory:http://java.sun.com/jaxp/xpath/dom" sys prop only in the __XPathFactory, ie. the prop for the default object model.