The problem isn’t what an engine will burn or certification, it’s distribution. I can put a LS6 in my plane today which uses unleaded pump gas (even 10% ethanol). I can have the latest mass produced engine technology using 30% less fuel, 1000 more hours until TBO and a quarter of the rebuild cost, but when I get to where I’m going they will only have 100LL, so you need to fix distribution before anything else. I can already get an STC for mogas for myo-470, but again… it’s not ANYWHERE. Like having a Tesla without a charging network, pretty useless - unless you never leave home.