The only
real alternative to 100LL in Europe are Diesel engines using Jet A-1. One has trouble getting 100LL fuel south and east of Germany/Austria even now - and I can only see the decrease in sell of Avgas, not an increase. I think the chance of getting a new gasoline on the market in Europe is highly unlikely, if not utopic.
Originally Posted by Jabawocky
It is 100% compatible with Avgas, in any mix you create. Take 999 gallons of Avgas and mix in 1 gallon of G100UL and you have have 1000 gallons of G100UL conforming fuel. Sure it has a TEL content still but it is a conforming fuel certified to go fly. So tank mixing, either in the ground or wing is not an issue.
With Thielert and AustroEngine engines you can use whichever mix of Diesel and Jet A-1 fuel you like (with respect to fuel temperature limitations of course) and you can get Jet A-1 basically everywhere in the world. Sadly, USA and Europe are light years away in the GA terms, but that's the world we live in.
Regarding the turbine engine - I think there isn't a turboprop (let alone turbojet) engine which has a comparable efficiency to a piston engine below 400 shp (which I believe this topic is discussing).