I do really think that draft releases should be public as there is no real reason for preventing people from outside the project team to see them before the release happens.
I help maintaining a (too) wide range of open-source projects and on some of them I do not even have core access. How can a user know which fixes would go into the next release if they do not see any draft when they visit the releases page? They have no clue about what was already merged and is expected to be part of the next release.
One very useful action used in conjunction with releases is the release drafter, which builds awesome release notes. Still, due to the fact that drafts are private that information is not available to the users.
MOVED TO Drafted release notes should be public instead of private · Discussion #4192 · github/feedback · GitHub as I suppose that may be a better place to send feedback.