The other problem with them is how the FAA figures out how much "fuel on board" is required to reserves.
Exactly the same way they do it today - number of minutes of flight time.
Greg Niehues - VAF 2018 dues paid
Garden City, TX
N16GN flying! http://websites.expercraft.com/airguy/
Built an off-plan 9A with too much fuel and too much HP. Should drop dead any minute now.