My girlfriend is extremely prone to motion sickness (can't even gently look around in a first person game using the mouse). Within a few short minutes becomes so dizzy and sick she has to lay down for like half an hour, and still feels the effects up to an hour after.
I myself felt some MAJOR motion sickness when trying my TiR 5 for the first time in IL-2, I had not set it up properly at all and it was totally messed up. Had to stop and rest. With anywhere approaching good settings I don't feel anything however.
If you look at the Spitfire in the Clouds video, it does look like they have this already. Especially when it pulls up near the end after hauling back hard on the stick for like 10 seconds straight (while also turning a bit) - coming out of this, the view is offset a lot upwards (which is otherwise only seen when pushing stick forward), and also a bit tilted/offset to the side.
Question is if this also applies to head tracking (Oh how I wish so - in IL-2 the headtracking is unaffected by the plane, it's like a fixed static point, with some vibration effects, and some not well implemented G-forces with the 6DoF mod).
Either way, it will need to be a slider so that users can tweak it to their liking. It depends on how your tracking is set up and how much you can tolerate before getting sick or thinking it looks really exaggerated messed up.