Is this kind of consumer revolt even really possible?
If you feel strongly enough that you refuse to fly altogether, then of course you can avoid flying on a 737 MAX. But I think most people did not feel the risk was that high. They just want to select "guarantee no 737 MAX" when booking a flight, and as far as I can tell that option doesn't exist.
Even if the flight is not a 737 MAX when you book, they can and sometimes do change aircraft, and as far as I know there's no option to get your money back when they do. If you show up and see it's a 737 MAX...you either get on or you lose your money, and have to find some other way to get where you're going, right?