Thanks for the reply on 100ll IO540 - so am I right in thinking you are saying any possible future disappearance of 100ll should not play any part in the decision making for purchase of an aircraft/share?
I think I am basically saying that if you can avoid 100L then do so, but the options for doing so are pretty limited and I would not touch any of them with a bargepole if I was going to do "real" flying, in a plane which I bought with my own money.
If OTOH I was running a flying school, and got some kind of "pay by the airborne hour" deal out of Diamond, then it would make a lot of sense because I would be protected from the diesel engine downtime which has brought many flying schools practically down to their knees.
Especially as training is exempt from the diesel fuel tax which is now payable on private flights and which has crippled the economic case for diesel retrofits.