One of the problems no one else mentioned so far is it takes TWICE as much alcohol to go what gas does. Carbureted engines require rejetting for alcohol and even then can't hardly run alcohol without highly modified carbs. Carbs designed for gas cannot flow enough fuel through the passgeways in the carb body to get enough fuel to not lean out the engine. The same can be said for EFI engines to a point. EFI engines set up for gas don't have large enough capacity injectors and are not mapped to pass enough alcohol at higher speeds/loads.
Ethanol, even smaller concentrations, can be death to aircooled engines. I discovered that with my motorcycle long ago when "Gasohol" first came out about '79. It just leans 'em out too much.
As far as putting the current 90/10 gas ethanol blend in the old stuff... I've had to go through the top ends of three engines recently where all the stuff the alcohol solved out of the old feul system wound up gluing the intake valve stems solid. I'd be happy to see E ZERO.
lastly... You see E85... I see 42% less MPG.