would be doable to add the text to the
resource-description of wsdl-url, related to the use of
jboss.undefined.host ?

The path
/deployment=/subsystem=webservices/endpoint=:read-resource-description

I ask that because HAL consumes and exposes the resource-description
of each attribute and having the help text about the
jboss.undefined.host in wsdl-host also helps CLI users.

A suggestion for the text:

"Webservice endpoint WSDL URL. If wsdl-host is set to
jbossws.undefined.host, Wildfly uses the requester's host when
rewriting the <soap:address>"