Nah, that wont work, or be really crappy image quality if it did. you already warped the image and lost many pixels of the view when going to oculus mode, you can't possibly convert that back to have the normal view. The best way is simply to have simultanious output of a normal screen mode as well. I imagine it would be no big deal if you have a separate graphics card for that, but it probably woulden't be too heavy for the hardware to do it on one as well if the engine supports that feature.(grab the image before it changes to oculus mode)
Somebody already did this with DK1 videos and the result was (IMHO) good enough for a stream. Then again, I don't watch streams so maybe you guys demand 1080p at all times!?
I believe the Crystal Cove demo had a box that did the de-oculus trick for the standard monitors they had at shows? I may be mis-remembering that though. If I remember it properly - if it's good enough for Oculus...
What you say makes sense though, but it seems a fairly niche feature that only those who make money off streams will be particularly bothered about.