I don't think MLS playoff format has much to do with the USMNT's failure to make the World Cup. Change for change's sake is not good either.
1. Many people have been asking for a format change for a while, this is not a new movement.
2. Correct, simply changing it doesn't guarantee more exciting games. But we aren't dealing with crazy, untested hypotheticals here. All these playoff formats have been tried around the world, we already know the pros and cons of each, including how well they induce excitement.
3. I'm lost at how invoking a criticism of the format in Europe is somehow a defense of using it here?
The knockouts are the most exciting games, no reason to shed them.
Also, there seems to be a tradeoff between playoff size. Increase the size, and many people complain that it devalues the regular season. But it never seems to be said that when reducing the size (to 8 of 28) will eliminate many more teams earlier, which makes the regular season less interesting.
Keep the middle 50% fighting for position until the last week. Then have them knock each other out in the first week of the playoffs.
Just like the "Hex," I also love the idea of fighting all year to get into the "Quads" or some other marketing term.