I'm betting the demand for auto-fuel STCs will spike sharply if this passes, and there will be more pressure brought against ethanol being added as a result.
Long term, relatively fuel agnostic engines like Diesels will replace AvGas engines in new planes.
If the certified plane biz folds, I'd expect that the amateur built experimental category would grow significantly, there's always going to be a demand for planes, and the experimentals aren't as centralized as the certifieds, so maybe they'd be less vulnerable to this. Being able to use auto-technology doesn't hurt either.
Monoculture can mean a strong herd of supercows, but the first virus that's shaped just-so can wipe 'em out to the very last. The same applies to any industry.