Sometimes releases are announced but get cancelled before they're released. Sometimes they're leaked and can be added to the database anyway, but not always. Depending on how soon before release it got cancelled, there can be quite a bit of information known, e.g. catalogue numbers (at least for the Japanese releases I work with) are often assigned well in advance. We have some cancelled releases with cover art. We've long stopped being solely about tracking actual releases, so it seems like this would be interesting information to have.

I sometimes come across these when working on label catalogues and I'm investigating missing catalogue numbers... right now I have no way of distinguishing a catalogue number assigned to a cancelled release which from a catalogue number for a release which just hasn't been added to the database yet.
We have some mentions of cancelled releases in https://musicbrainz.org/search?query=cancelled&type=annotation&method=indexed
HibiscusKazeneko has a bunch listed on https://wiki.musicbrainz.org/User:HibiscusKazeneko/Releases_that_cannot_be_added
VGMdb also tracks cancelled releases - https://duckduckgo.com/?q=site:vgmdb.net+cancelled

If we do add this, "cancelled before release" might be a better name to use, or I could see people using it for things like out of print releases.