Getting to what you describe shouldn't be a huge hurdle; things already largely work this way in AS 5, it's just that the core JGroups and JBC related services, like everything else, are in their own config files. People don't configure a JGroups stack in container configuration files or annotations; at most they indicate what named cache config to use from a centralized set managed by the CacheManager service; that cache config specifies the name of the JGroups stack to use, which again comes from a centralized set from the ChannelFactory service. Those centralized sets are logically under the control of an admin.
The stuff I was talking about when I said "the details of what needs to be configured are often disparate between different services, so I'm not sure those configs can profitably be externalized into some common configuration element" was things like load balance policies for remote EJBs, eviction configurations for entity caches, etc.