That gives it the passive Blackout*on a 3 minute cooldown. This would be a nice alternative to creating a broad, 8th item slot for red wards, and would give more tools for the support to control the vision game. I'm suggesting a double-time CD compared to DB because it needs to have some negative.
Furthermore, supports are already managing a considerable amount of active cooldowns. Putting this in would allow them to stay on top of the vision clearing game without having to maintain an open slot for Reds.