If this returns a pointer to a service registration, what is a service registration?  If this is something that an application (or even the aggregator) needs to keep track of and supply back (like for `unregisterService`) similar to OSGi's `ServiceRegistration` interface, then we should have an explicit interface so that those functions only accept arguments of type `ServiceRegistration`.  Keeping them as Object would let someone pass any object into the method and that's not something we want to be ambiguous about.