Use Index Resource to Get Entity Fields

The index resources only return the fields (column names) from that particular entity type's table. Is it possible to get the index resources to include entity fields as well?

For example, the comment index resource by default just returns all the fields/columns from the comment table. Is it possible to include the comment_body field in the results?

I'm aware of the services_views and views_datasource modules and how they can be used to get custom fields. I'm just wondering if there is a particular index query that can be passed to the index resource, or if there are any services hooks that can be used to include an entity's fields with the index resource results.