There are too many people already doing arches, dashboards, etc, but I see potential for aerodynamic aids, front and rear, that, if possible, will fit over the bumpers, so you can keep some body protection in the event of minor bumps. Or, the mouldings could be foam filled and provide a superior bumper function as well as improving aerodynamics, but they would make the car longer. Issigonis would turn in his grave. Apparently he was rather upset when the Mini turned out to be 1/4" over his 10 feet target. I don't know why he did not just have the bumpers flattened slightly, maybe internal BMC politics got in the way.
Also, a roof rear edge spoiler may be beneficial in reducing drag.
Such things ideally need input from an aerodynamicist and some wind tunnel testing, so development would not be cheap, but I do think that there is room for such things in the market even now.