It so happens I read this after attending a Flight Safety Forum in Sydney today. One of the speakers was a petrochemist from Shell and I asked him about the future in store for all the aircraft piston engines as the high lead fuels are withdrawn.
To summarize, it is his considered opinion that the lower power engines, up to maybe 200hp will run OK on 80 Octane fuel. Higher power engines will simply not be operable, and the private / freight / charter operators will simply have to re-equip with turbines or diesels if available.
When I asked about the operators of vintage aircraft, such as we all like to watch at the airshows, his answer was effectively a shrug of the shoulders and a statement that they would not be able to be flown. He did add that there may be some sort of ‘synthetic’ possibly non oil derived fuel available in small quantities, but was not optimistic.
Not very encouraging at all really!