I thing this leads in the wrong direction due to the nature of roadmaps being a high level and very rough view. We should strive to eliminate dependencies and not put them on a roadmap too.

We should handle dependencies in the Program Board and on team level, but not spread them to roadmap.

Actually, this would come in very handy on all roadmaps and breakouts on any level, once they are released.

indicators like on Team-Breakout Boards would be nice :)