MusicKit additional properties for Songs and Albums

Hi,

I know MusicKit is in beta, but after having talked to an engineer at a WWDC lab, it seems to be feature complete for now. I really enjoy the framework and it helps wrap the Apple Music API nicely. However, the types it provides are missing some properties that are relevant to any music item (song, album, music video) such as the releaseDate, contentRating, durationInMillis and url.

This is the JSON response from a /tracks relationship of an album:

        "previews": [
          {
            "url": "https://audio-ssl.itunes.apple.com/itunes-assets/AudioPreview115/v4/e6/84/62/e6846266-2779-4527-902b-0a3b6f73be75/mzaf_18277320986443617976.plus.aac.p.m4a"
          }
        ],
        "artwork": {
          "width": 3000,
          "height": 3000,
          "url": "https://is1-ssl.mzstatic.com/image/thumb/Music124/v4/c4/7a/01/c47a01c2-2b04-a327-12bd-c726ae076c7f/886447823545.jpg/{w}x{h}bb.jpeg",
          "bgColor": "1c1c1c",
          "textColor1": "fafafa",
          "textColor2": "e1e1e1",
          "textColor3": "cdcdcd",
          "textColor4": "b9b9b9"
        },
        "artistName": "Kollegah",
        "url": "https://music.apple.com/de/album/alpha/1477896577?i=1477896820",
        "discNumber": 1,
        "genreNames": [
          "Hip-Hop/Rap",
          "Musik"
        ],
        "durationInMillis": 141827,
        "releaseDate": "2014-05-09",
        "name": "Alpha",
        "isrc": "DEDG61400001",
        "hasLyrics": true,
        "albumName": "King",
        "playParams": {
          "id": "1477896820",
          "kind": "song"
        },
        "trackNumber": 1,
        "composerName": "Kai Engelmann, Phillip Herwig, Alexis Papadimitriou, Daniel Coros, Yunus Cimen & Sadik Kalyon",
        "contentRating": "explicit"
      }

As you can see, the releaseDate, durationInMillis, url, contentRating, etc. are missing from the struct Song : MusicItem in the MusicKit.

I was wondering if we can extend MusicKit as developers in a way to include the releaseDate and other types or are we making a choice between using custom models and custom requests vs. using MusicKit?

Thanks