Replacement fuel for leaded avgas will have to accommodate the airframe which is more of a problem (and could be more costly) than the engine modifications. Who is going to pay for all the testing in each and every current airframe so as to be able to use an alternate fuel? Seems to me like a lot of planes will be useless/worthless without certified fuel to operate them? Imagine what alcohol will do to a "wet wing" after a few years ?