Another approach I've been wondering about is a spyder section made from carbon fiber with carbon fiber matrix/foam core. The relative strength compared to other materials including chrome moly steel is shown in the link below.
This approach could potentially provide significant upgrade to the overall strength of the driver/passenger area without the intrusion of an internal cage with its inherent safety risks. As mentioned before the potential improvements to overall chassis stiffness could also be significant.
Apart from the difficulties of manufacturing such a component in carbon/carbon, the other issue would be to find a way to provide a mechanically strong interface between the spyder and the base of the front pillars and to the rear bulkhead.
Apart from the difficulties of manufacturing such a component in carbon/carbon, the other issue would be to find a way to provide a mechanically strong interface between the spyder and the base of the front pillars and to the rear bulkhead.