How about... when the game wants to do something sickness-inducing, such as turning your head with the mouse or right analog stick, sidestepping, running at 30km/h, etc. the game shrinks down the FOV to a small fraction while that action is happening. Or perhaps even shows some sort of frame around your view. But only while that action is happening.
For example, you don't get motion sick (as much) playing computer games on a laptop screen. Because your visual senses tell you that you are not actually moving, and it's just a small image you are looking at which is moving. The part of your view outside the screen frame grounds you.
The same trick should work on the Rift, if you applied it well. And if you only apply it when necessary, you don't have to sacrifice immersion or visual field the rest of the time.
Recall what I proposed on the MTBS forum, regarding COD-like action games. To have a bar in the peripheral that indicated the direction of rotation, and/or attack, the bar becomes stronger at faster turn rates, more defined at faster turn rates.
In this way, the brain has a visual anchor of some sort, during the motion. Just another method to try out and see what happens.
Intelligence... is not inherent - it is a point in understanding. Q: When does a fire become self sustaining?
It sounds good to me too. It is the unexpected motion in your peripheral vision that seems to be the biggest problem. Using "tunnel vision" during non-vestibular turning is worth exploring. It should work very well for some people, and perhaps many people.
Honestly i heard about the new Oculus prototype and it seems will no longer have motion sickness,so maybe isn't very necessary this kind of adjustment,especially if it reduce also a little bit the immersion experience.