As a non European, it appears to me that the required fuel is now becoming the dividing line. I was flying in Europe last week. The only airport which sold the required 100LL was a 40 minute flight from home base. The landing fee at that airport, was about half the cost of filling my 150 here at home. I did not buy the fuel for the plane, so I have no idea of it's cost!
Chicken and egg, I see the core of GA aircraft (the single Cessnas and Pipers) declining, so it now gets even more divided to Jet fuel or mogas burners. If GA in Europe is not declining, it's at least becoming a lot more compartmentalized by type....