Hello Vladimir and Jean,
In addition to avoiding class references, we also have a requirement that the user configuration only reflect user settings (and not our internal wiring like in the past). The configuration is extensible though, so a user can add new "subsystems" to their domain.xml by specifying the extension that adds it.
A subsystem provides its own custom schema for its section (with a goal of being friendly and type safe) and it also maintains a detyped representation which is used for all of the vairous management interfaces. So in a nutshell, anything that integrates with AS7 via a subsystem is fully manageable (and consistent with the configuration).
A subsystem is also responsible for acting upon the management operations (note that configuration when parsed generates the very same management operations) to make the appropriate changes in the runtime state of the server (if not possible it tells the system a restart is in order). This is where you would create new services, launch tasks etc.
So for mobicents I would recommend a subsystem (although you can have more than one if you want) that uses JBossWeb SPIs to launch your SIP server. This should give you essentially the same reuse you had before. It would also make sure the SPIs best represent what you are wanting to achieve. Lastly, it would provide a really nice easy to use configuration that would immediately be available in all of our managment interfaces (java remote protocols, HTTP/JSON protocol, embedded console, JON, etc).
One thing though I should warn you about is that we are currently making the transition to the detyped model (which was done to make life easier for jbosstools and JON and the console), but that work is in a special detyped branch on Brians tree. We hope to migrate it as fast as humanly possible, however you may want to either base your work on that, or to instead wait until we formally merge it upstream. If you go with the latter you could probably initially focus on working with Remy on the JBossWeb SPI contracts that you currently have and need.
Thanks!