Welcome aboard :)
It is expected that "player" use case will be consumed in media libraries/playlist etc, as we will also specify the playback/sync events via postMessage, similar to the ones YouTube/Vimeo/SoundCloud got already.
The spec will be constantly expanding though, as it is easier to add than it is to change. We start with the ones that are already available by publishers (logo, thumbnail, player, reader) and that we've verified a lot of implementations of and can document.
If you'd like your use case to be included into initial version too, please, submit an issue to the repo and we'll discuss it there. We see various other scenarios as well, but it takes community to come up with exact use case.
For now, "reader" will probably work well for you. Iframely returns "reader" for Twitter statuses, for example (and it will change when we have a better use case).