This is only for content that you can actually play through MC. Locked-down services like Netflix or Disney+ do not allow any kind of integration.
The goal is to be able to integrate anything that has a URL that you can actually play in MC, without having to use a potentially cumbersome website to navigate.
This is YouTube, Twitch et al. With the option for a login and personalized feeds, if the website has a proper API for that. Easily extensible without knowing too much about MCs internal workings.
Nothing of this is being stored in the library, since all this data is potentially transient. At most it gets into Playing Now when you are currently playing something.
The first bundled plugins will be for YouTube and Twitch. We hope to be able to design them simple enough to be able to make creating custom plugins for all sorts of services, video and music alike, pretty easy.
And once we have a Python scripting layer in place, we can also extend that to other areas in the future.