To prepare for the external API and as a general improvement, we extended the publication element to contain sub-elements of tracks, catalogs and attachment. With the current solution it wasn't possible to know which elements have been published for the given publication element. Only by asking the related services (e.g. search service for engage publications) it was possible to get them. This change needed some changes in the core components of the media package elements and to make it visible in the new UI we added it completely to the new elastic search index.
Especially for third-party systems which don't have direct access to the given services or shouldn't even have knowledge about this services, it make much more sense to get the whole information from a single endpoint. This endpoint is reading everything from the index to perform fast and avoids additional service calls.