Without knowing full details, it seems like it operates somewhat similar (in spirit) to an app called Shou ("show"). With Shou, you can record the screen from your iOS or Android device, and broadcast it online. Your subsequent screencasts are then saved.
For instance: https://shou.tv/parrottvision (The site is rather difficult to navigate. Click the handle on the top left to get the 'Videos' link, which takes you to his most recent one. Then browse the list of videos with the handle on the top-right. I recommend the ones from late March/early April).
This is also good for those who want to see the Pilot app in action.
Anyway, with this YouTube integration, it would seem that it simply pushes your LightBridge preview video (with telemetry overlay? Who knows) to YouTube. Obviously, you'll need internet access from your device (perhaps wifi will work if you're in range, since it won't use your WiFi for the Phantom?)
Sure, there are always delays when dealing with the internet. Shou is about 15 - 20 seconds, depending on your connection and the alignment of the planets.
Of course, Shou is in Hong Kong, and is not YouTube, so I would have to imagine that the latency will be much less with this upcoming feature.
That might be your only way to send the display to a second device, seeing as the LightBridge in the transmitter only has a USB port (still curious if we'll see successful hacks in drilling out a hole and installing an HDMI connector to the circuit board, or if they'll make a completely new LB)