That didn't take too long. After several weeks of testing, Instagram has given all mobile users the option to add a guest to their live broadcast. Tap an icon and you can invite one of your viewers to participate, splitting the view in two. You can swap guests at any time, and these group videos can either disappear right away or live a while longer as Stories in your friends' feeds. Friends can tell that it's a two-person stream with a quick glance at the Stories bar.
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.