At the moment the issue is the desktop window is a MUCH smaller FOV than what you see in the headset or that a normal player would see on their desktop. If you search for streaming here you'll find a thread that details how to setup a second window on your desktop that will have a much higher FOV than the standard window. The issue with that though is that it's essentially what one of your eyes is seeing and as such it's tall and skinny like video from a cell phone. So you then would have to take that into OBS and crop it some to make it full frame.
In the forthcoming 2.2 the desktop window has a near normal FOV (I can't swear it is normal but it seems it) so once that's released it'll make streaming while in VR much easier. When you run the second window on your desktop it definitely gives you a performance hit. The other thing to realize is that VR tracks all the tiny movements you make with your head - in game you don't notice this at all as the refresh rate is so high it looks very smooth to you. However the external view on your desktop, the one that would be streamed is extremely jerky and very difficult to watch. The current VR streamers have to make sure to keep their heads as still as possible and move as smoothly as possible so they don't make the viewer sick or annoyed. While Youtube can fix camera shake once a video is uploaded there isn't anything that does it in real-time - at least not yet.