I don't know what ever became of the line of research, but there was a very interesting book I read decades ago called Descartes' Error by Antonio Damasio that examined case studies of patients who had their corpus collosum severed, resulting in a split brain. You could show their left and right eyes different images and ask them what they saw and they would write and speak different answers, because speech and writing are controlled by different brain hemispheres.
This seems to suggest that any bottleneck in conscious attention is not an inherent limitation of an animal brain but rather a consensus mechanism we've developed to keep our chain of experience coherent. If we get rid of the constraint that all of our external communication channels need to present the same narrative, we can seemingly process more information even when it requires being a conscious center of attention.
It's like UIs being single-threaded, because otherwise you would have chaos if several background threads are trying to update the UI at the same time.
This seems to suggest that any bottleneck in conscious attention is not an inherent limitation of an animal brain but rather a consensus mechanism we've developed to keep our chain of experience coherent. If we get rid of the constraint that all of our external communication channels need to present the same narrative, we can seemingly process more information even when it requires being a conscious center of attention.