Whilst MusicBrainz does not allow release groups to be marked as bootleg releases, releases themselves can be. I’d like bootleg releases to be given the same separation as implemented for singles, compilations, live albums, EPs, etc have been.
Example of a bootleg release: https://musicbrainz.org/release/1fac2591-4414-4f62-89a2-6372f4c81dc7
IIRC, this isn’t so much information about the release but another type of categorization.
Musicbrainz supports a Status for releases with values like Official, Promotion, Bootleg, Pseudo-Release, Withdrawn and Cancelled.
The current release types recognized by Plex are made up by the primary/secondary types of a release / release group
https://musicbrainz.org/doc/Release_Group/Type
This shouldn’t diminish your suggestion – just trying to give some context and pointing out “it might not be that simple” 
Yep, I completely understand. Separating bootleg/unofficial releases from proper ones, however, is something I think most would desire, for the same reason as separating singles from studio albums.
I do think MusicBrainz ought to have a secondary release type for bootleg material, but that’s an upstream issue (and one that probably won’t be considered).
I would love for Plexamp to support the Bootleg release type metadata. I have a few bands that I like to collect various concert bootlegs from. It would be nice to have the official live albums separated from the piles of bootlegs when browsing the library.
