GitHost.io will be shut down on June 1, 2019. At that point this instance will be unreachable and all data will be irrevocably deleted. More details at https://about.gitlab.com/gitlab-hosted/#githost-is-shutting-down-on-june-1st-2019
Which streams should be put under ModeratedNoticeStream is probably open to debate. But at least the public ones should hide the posts from users that are sandboxed.