Extend the "commands" to include built-in idMso for use in custom groups and tabs as well as repurposing
In the COM world using Ribbon XML it's possible to: 1) display built-in buttons in custom groups and 2) re-purpose built-in buttons. This way the UI can be optimized for the purposes of an add-in. (2) is especially important because Office applications don't expose very many events, making it difficult to impossible to know when a user has done something that requires a reaction from the add-in. In this regard, COM add-ins and VBA are still much more powerful than the JS APIs.