If the EPA/NHTSA/DOT ever wake up from their Rip Van Winkle slumber,they may begin to smell efficiencies which lay beyond the current 5-foot maximum length restriction.
Perhaps we could 'start' with 5-ft,and offer the full Monty afterwards,when the government learns the definition of 'protection.'
So far they still prefer bodybags and flag-draped coffins.