What if they moved their speed record attempt to Salar de Uyuni in southwestern Bolvia?
At 12,000 feet above sea level, higherdensity altitude would help reduce aerodynamic drag. If they ran on a hot day, density altitudes might exceed 20,000 feet MSL. They could exceed sea level numbers (miles per hour or kilometres per hour) while still reducing risk by remaining sub-sonic.
Have they also considered that modern electronic advances would allow they to simplify external mold lines while reducing risk to human drivers?
Back in 1992, I helped Manley Butler build a specialized parachute for a NASA program related to supersonic transport airplanes. Instead of the Concordes' complex hinged nose, they installed a video camera under the nose of a NASA two-seater TF-104 Starfighter. The back-seater pilot was going to fly a series of landing approaches while watching the runway through the camera.
If you install a video camera in the nose of a land-speed-record car, you only need to worry about designing the nose for best air flow. If the driver still wants peripheral vision, just install a few sideways-facing cameras and more video screens along the sides of the cockpit.
Modern electronics also allow them to remotely-pilot the first few test runs. Once they prove that the car will remain stable at close to super-sonic speeds, they can install a driver to collect the glory.
Unlike an aircraft, this thing runs on wheels, on a relatively rough surface. If you look at the in-car footage, there's a lot of driver input keeping the thing straight. I doubt you could do that by remote control, even with a state of the art "autopilot".
Cars are much harder than airplanes. Reality is dude is lucky. Most Aerodynamics don’t ever get to be solo designers. They are mostly figuring out how much a bolt head can stay exposed in an engine pylon designed thirty years ago.