Here's something pretty cool that YouTube is currently testing. Pretty soon, you might be able to see how many people are watching the same video as you're watching at the same time. Spotted by Android Police, it seems that YouTube is testing a new feature that will show concurrent viewer counts.
Right now, it appears that the feature is only live for select Android users. As you can see from the screenshot below, you will be able to see concurrent viewer count just below the video title. It works the same way as you're watching a live stream, such as a Twitch stream.
While this is beneficial for viewers, this could also prove to be useful for content creators. You can see how many people are viewing you videos at a given time, be able to see when people view your videos often and when they don't. Since YouTube is working on this feature, it's also possible that they may provide some additional analytic tools for content creators.