I'm not following your reasoning about the common denominator, not sure we're on the same wavelength about what I meant. I'm claiming that in order for an application to be "reclaimable", you have to be able to access and manipulate the data under the app. Some applications currently work that way now, lots of them don't.
For example, we can "reclaim" non-DRM ebook readers, audiobooks, and music players that play local files or use an open API. But a company-specific walled garden streaming DRM'd ecosystem will be almost impossible to build around.
You're talking about entire systems. That's something to be optimistic about too. But it's actually not the thing the comment you responded to was about. I'm not saying I'm excited to get out of the Apple Music ecosystem (I like Apple Music, the service, quite a lot). I'm excited to get out of Music.app, and into my own custom Apple Music player; one where playlists and play history are simple, sanely-schemaed sqlite databases.
I gotta be careful, I'm going to talk myself into staying up late tonight building that.