On the binding configurations, the socket-binding-group in domain.xml exists to:
1) Allow sharing of a bunch of configurations across multiple server groups via a simple reference.
2) Make it easier to start multiple servers on the same machine bound to the same interface by applying a simple port offset to the socket-binding-group.
These don't cleanly apply to the DC, since there's only one DC. Cleaner I think is to stick to having the elements that need to configure a socket expose an attribute that takes an interface name (since the same named interface may be used elsewhere in host.xml) and another attribute specifying the port.
The downside is if users want to avoid port conflicts with regular servers on the same host, they need to pick non-standard port values (e.g. don't use 8080 for HTTP). Perhaps we should have default values for the different ports that are non-conflicting with standard values.