The problem is, "legalizing" it is like 0.1% of the work. The hard part is all the testing/certification you have to do for every single aircraft and engine design.
> The FAA signed on September 1 supplemental type certificates that allow General Aviation Modifications Inc.’s 100-octane unleaded fuel (G100UL) to be used in every general aviation spark-ignition engine and every airframe powered by those engines.
All piston engines and aircraft are certified for G100UL.
It’s actually very easy if you are the government; you just say from 5 years from now, using lead fuel is banned. And then someone else has to do the work.
> The FAA signed on September 1 supplemental type certificates that allow General Aviation Modifications Inc.’s 100-octane unleaded fuel (G100UL) to be used in every general aviation spark-ignition engine and every airframe powered by those engines.
All piston engines and aircraft are certified for G100UL.