The engines are visibly different. They are huge.
I am not an industry insider but my understanding is the vast majority of the flying public simply does not matter. We are flying on the cheapest possible ticket. The people who do matter imo are those who are flying on a corporate account or better yet those who control a corporate account. If wealthy people refuse to fly on this death trap, I think airlines will listen.
This also means that once Boeing gets the 737-8200 (or whatever) approved for flight, it will be unnoticed for customers who won’t ever notice the difference between it and an 800 or an A320.