Also two words: Crumple zones. You don’t want a super hard Skelton, that will only increase crash forces.

No shit, that's why I mention a helmet.

Roll cages, if properly done, do not affect crumple zones. The passenger compartment should not be crumbling and that's the only part a roll cage should be in. Keep in mind that actual race cars have a rigid occupant compartment, crash at higher speeds, and have great safety records due in part to the protection offered from a harness, helmet, and hans. On the other hand, airbags are more prone to failure and can injure or even kill people.

The only reason I mention a roll cage is because it would be for dual use. You could use a helmet/hans in place of an airbag in a regular street car and would likely be safer. Again, the only reasons we have for not doing that is that some people don't use their seat belts and most people would find it inconvenient.