You should see the feature in version 20 of Instagram's apps for both Android and iOS. Instagram is pitching this primarily as a way to make live streams more social, but we can see this being particularly useful for celebs and social media pros. A musician could invite a fan for a virtual meet-and-greet, while a news outlet could use it for joint reports or discussions with viewers. You're not about to see professional interviews (not when Stories vanish within a day), but this makes Instagram's live video considerably more useful -- or at least, not quite so lonely.