There are also some interesting accounts of research into biomass based fuels that can replace LL100 and of course there is a production version of the Embraer Ipanema which runs on ethanol.
Embraer EMB 202 Ipanema - Wikipedia, the free encyclopedia.
I have heard that in Sweden there is a group who have started a limited manufacture of the older version of avgas without the led additive. It is claimed that older engine designs still in use today were originally intended to run on this fuel and will operate better with it and suffer from less plug fowling and other problems.
Moving away from LL100 to Jet A1 reduces cost in the supply chain since Jet A1 benefits from a larger scale of production and lower tax than LL100. The use of Jet A1 for European GA isn’t only motivated by ecology but also by costs. These two issues come together for this particular fuel option. The belief is that it offeres a cleaner technology that operates at a lower cost than LL100.