Alessio,
in future we are probably going to see less deployment chains, possibly just one. The web subsystem should be enabled to setup endpoints based metadata that you attach to the DeploymentUnitContext. A (better) alternative would be that the WS DUP registers a WSService that has a dependency on some JBossWebService. When WSService activated it uses well defined/stable API from the JBossWebService to setup a web endpoint.
IMHO, this is generally needed because other subsystems like the OSGi HttpService may also need to setup Http endpoints through API. Perhaps you can use
[JBOSGI-308] Implement the HttpService ontop of JBossWeb
as the entry point to this discussion. In short, JBossWeb would need to expose a set of well defined services that allows others to setup endpoints.