Whats wrong with 100LL until a proven substitute is found (nothing). This is purely politically driven for people that hate aviation freedoms and want nothing more then to take everything away, its called power by force. If someone can come up with an unleaded fuel that’s cheaper and works for all, can store in a plane for 5 years or more and is readily available and easier to make then there won’t be any problem with the transition. Just like electric cars, windmills and mother Mary that can grant you your every stupid wish, its a pie in the sky and a fools paradise. Let capitalism work and the best idea win without true idiot bureaucrats ruining everything.