It would be great to have checkbox in repository configuration, together with "Allow forks" that would add to all forks same read visibility as original repository.
Use case is following: We have main repos that are used for builds, etc. Users that want to contribute are motivated to create forks, work on their changes there and then create pull request from their fork to main repo. However many reviewers want to checkout such branch locally and build it/browse it using IDE/run other tools there. This is not possible by default, as all forks are private. We think that as main repo has some visibility, all possible changes to it should have same visibility so everyone could review those changes by themselves locally, taking advantage of any tools they are using.