Support environment variables in node-type element in Configuration of Modeshape Wildfly Subsystem

It would be nice to support environment variables in the node-type XML Element in the Modeshape Subsystem Configuration for Wildfly.

The following entry in standalone.xml leads to "WFLYCTL0264: node-types may not be ModelType.EXPRESSION":

<node-types>  
    <node-type>${jboss.server.config.dir}/modeshape/content-node-definition.cnd</node-type>  
</node-types>  

The following is possible for initial-content in standalone.xml:

<workspace name="my-workspace">  
    <initial-content>${jboss.server.config.dir}/modeshape/my-initial-content.xml</initial-content>  
</workspace>