Automatic Dependency/Blocked issues/notifications
Some issues have great ideas in them, but should be left alone until feature/issue X or Y has been implemented/closed.
Proposal
Like in gantt charts you can make tasks dependent on something else, or unable to start until that previous task has been completed.
Have a similar functionality within gitlab with a slash command and a persistent system note at the very bottom of an issue, which tells everyone this issue is waiting on something else.
Also when the system sees that the dependency issues are closed it will re notify every participant within that issue thread.