Graduated approach ignores the decades that have ALREADY been provided as an exception to the lead fuel rules that apply everywhere else - it's already been graduated.
Start at 10% with a commitment to ratchet it up by 4% per year or something. That's enough to start an immediate reduction without destroying the industry.
If you're making choices about engine overhaul now for an overhaul that will last you 7-8 years of light use, fuel costing 40% more at the end of that overhaul will definitely get your attention.
> it's already been graduated.
Doing nothing for decades when it was impossible; and then doing nothing for a decade or two when transition became possible; and then pushing the industry off the cliff is not graduated.
Perhaps that's wrong, but I distinctly remember the statistic and it stuck with me.
If you threw a few billion more at leaded paint remediation, I think you'd make much more of a difference. I think the aviation lead problem should get fixed, but because it's such a small part of the overall problem it makes sense to take a graduated approach instead of giving GA businesses the death penalty. Tax leaded aviation fuels, and use the proceeds to pay for leaded paint remediation.