I've seen the video, and it is the primary reason of why I'm considering the 6S+. Although one thing I noticed from trying it in the store earlier is that 4K videos are less stable than 1080p ones. Video recording in 1080p definitely is "smoother", if that makes any sense. Is it because of the frame rate? Also you cannot really see a difference on playing 4k videos in 1080p-display phone right? The same goes for the 760p of the 6s. You need an external display that supports 4K to really see the quality difference.
A good point a user in another forum did make though is this:
"I have a theory on this. Maybe OIS is included on the 6 Plus because you're more likely to have a shaky hand holding the bigger device as opposed to the 6/6S and it happens to be convenient enough to be one of the reasons to justify the price difference."