Generally, the higher the compression, the more restrictive the fuel.
I see there is spec for 100VLL fuel which is allowed where LL is allowed (19% less lead than LL). I've never seen that for sale? Certified in 2011 apparently
http://www.aero-news.net/index.cfm?do=m ... fc46644a58 From what I hear, VLL meets the spec for LL (as LL specifies a maximum amount of lead and the new standard specifies a lower maximum) so what we are getting sold and are using may already be meeting the VLL spec?
On health, the amount of lead put into the atmosphere used by aviation is tiny compared to what used to be put out by cars, but aviation is now the largest source of TEL in the atmosphere.
The removal of TEL from cars, for the entire US population, during and after the TEL phaseout, the mean blood lead level dropped from 16 μg/dL in 1976 to only 3 μg/dL in 1991, with "elevated" levels said to be above 10 μg/dL.
There have been measured health benefits (average IQ increase across the world) attributed to this.
There has been measurement of lead levels in kids near busy GA airfields and they show a higher level than those who don't live near busy GA airfields. However the numbers aren't particularly significant (although I can't find the studies mentioned by various people such as here:
https://www.scientificamerican.com/arti ... tion-fuel/ ). I haven't seen studies of pilots.
I'd say that lower lead is a good thing in aviation fuel. However it really doesn't feel changing will make a significant enough difference to the world for it to be mandated.