While I understand where you're coming from, I think the jerky motion only adds to the realism of the NFSS cockpit view and I wish GT would take a page of EA's book (I can't believe I just said that). Racing isn't sterile and smooth...your head is bouncing around, your neck hurts, there's tire smoke in the cabin, it's 110 degrees with the heat off the engine...NFSS has overdone sounds and the physics are all wrong, but the visuals in the cockpit blew me away. I look at GT5 cockpit view videos and it's as if my head is nailed into the seat.
I very much hope PD devs at least think about this with GT5's kart races. I was lucky enough recently to have an afternoon in a two-stroke shifter kart and while it may have been partly the fault of the track, it was an incredibly violent experience.