AOPA’s Tom Haines reported today that after an effort lasting decades, GAMI has received two STCs for the use of its G100UL high-octane unleaded Avgas. The article – linked to below – cautions that one STC currently applies to a limited number of Lycoming engines and the other covers a limited number of Cessna airframes.
But they have a foot in the door and it’s a whole lot easier to expand the AML (Approved Model List) than it is to get the initial STC. Who knows, we may see a solution yet.
https://www.aopa.org/news-and-media/all-news/2021/july/27/gami-receives-unleaded-avgas-stc