The upcoming #faircamp release will feature "unlisted releases", that is, you can add the flag "unlisted" to the release manifest/section to hide it from all publicly accessible pages, while still being able to visit the page if you know the permalink.
There are some minor implications for label mode though, which I'd be happy to have double-checked - if you're a (current or potential) faircamp site operator, do you have any thoughts on this?
"An unlisted release is never visible on the home/index page.
In label mode there are some additional intricacies: An artist that has only unlisted releases is not visible on the home/index page, but in turn, all of these unlisted releases are visible on the artist page, as the artist page itself is implicitly unlisted then. If however, an artist has even just a single listed release, it becomes visible on the home/index page, and on the artist page itself all unlisted releases are not visible anymore."
