Yes, I'm inclined to believe such an "in-between" might possibly arise from Iain McGilchrist's line of research into the difference between the brain hemispheres and the relatively recent dominance of left-hemispheric thinking in society. I always highly recommend his book 'The Master and His Emissary' as a follow up to anyone interested in Jaynes' ideas. While it doesn't necessarily imply the full spectrum of schizophrenic-like symptoms in early peoples the way 'The Bicameral Mind' did, it's presentation of right-hemisphere driven societies of the past isn't a far leap from what Jaynes seemed to be grasping at.