George: You could either show existing data that proves that G100UL is safe for use in aircraft, storage tanks, fuel trucks, barges, pipelines, railroad cars, etc., or you could submit G100UL for extensive testing in this regard (something akin to what EAGLE is requiring). You really have no other options. I am afraid that anecdotal information about one plane or the other being okay with G100UL is not particularly convincing. That is not my opinion, but appears to be the opinion of the shippers who will not touch the fuel, as well as Cirrus and Lycoming.
You apparently chose a very reactive octane booster for G100UL, maybe one that others have considered but have avoided. To compound this, you chose the STC/no-ASTM route, which, with little doubt, has less rigorous requirements for proving materials compatibility than the other routes. Again, I emphasize that EAGLE is requiring materials testing on some 160 different materials. Why are you surprised by some skepticism in regard to the materials compatibility of G100UL?